chore: image apk upgrade optimization

[daanschipper]

Fetching updates in memory to not leave anything on disk. Use one RUN command to avoid creating two separate layers.

See diff below, 4 instead of 5 layers, no apk cache in the image.

Description

Before

❯ docker inspect docker.io/aquasecurity/trivy-operator:dev-before                                                                                                                                                                                                                                                                                                                                                                        
[                                                                                                                                                                                                                                                                                                                                                                                                                                        
    {                                                                                                                                                                                                                                                                                                                                                                                                                                    
        ...                                                                                                                                                                                                                                                                                                                                                                                                                
        "RootFS": {                                                                                                                                                                                                                                                                                                                                                                                                                      
            "Type": "layers",                                                                                                                                                                                                                                                                                                                                                                                                            
            "Layers": [                                                                                                                                                                                                                                                                                                                                                                                                                  
                "sha256:256f393e029fa2063d8c93720da36a74a032bed3355a2bc3e313ad12f8bde9d1",                                                                                                                                                                                                                                                                                                                                               
                "sha256:5ce487bc8286974c83e1a26379f4a1facf68349abdab37a203efea4b0634afa6",                                                                                                                                                                                                                                                                                                                                               
                "sha256:9f0d01bd0aa501d7778e5b05cfddae2036c7156c0b6a313f01891de7b8191aa8",                                                                                                                                                                                                                                                                                                                                               
                "sha256:4021271c563cea6e7dcd28988e8eab1b42a549b8adc8d1f32b5b0187b71fef18",                                                                                                                                                                                                                                                                                                                                               
                "sha256:f01e3423333a509d7e33b6a6e9d28178c039733390d624fd8c978b520691de79"                                                                                                                                                                                                                                                                                                                                                
            ]                                                                                                                                                                                                                                                                                                                                                                                                                            
        },                                                                                                                                                                                                                                                                                                                                                                                                                               

❯ docker run -it --rm --entrypoint /bin/sh docker.io/aquasecurity/trivy-operator:dev-before
/ $ ls -la /var/cache/apk
total 2552
drwxr-xr-x    1 root     root          4096 Dec  1 11:46 .
drwxr-xr-x    1 root     root          4096 Oct  8 09:28 ..
-rw-r--r--    1 root     root        500031 Dec  1 11:46 APKINDEX.6c16d705.tar.gz
-rw-r--r--    1 root     root       2094055 Dec  1 11:46 APKINDEX.76ae5dea.tar.gz
/ $ 

After

❯ docker inspect docker.io/aquasecurity/trivy-operator:dev                                                                                                                                                                                                                                                                                                                                                                               
[                                                                                                                                                                                                                                                                                                                                                                                                                                        
    {                                                                                                                                                                                                                                                                                                                                                                                                                                    
        ...
        "RootFS": {
            "Type": "layers",
            "Layers": [
                "sha256:256f393e029fa2063d8c93720da36a74a032bed3355a2bc3e313ad12f8bde9d1",
                "sha256:956bcb29dfac86b83223585559fa9f229d02bc00316628185988c5e2a425309c",
                "sha256:ef49bf7d1228d61d00e3de3b04934c55bd3c5370b9963a1056c8cfbd9067f8aa",
                "sha256:f68455b00b927699b3d3d0595f2152aff98ce639f63ae60ca51b8b6af801a280"
            ]
        },
]

❯ docker run -it --rm --entrypoint /bin/sh docker.io/aquasecurity/trivy-operator:dev       
/ $ ls -la /var/cache/apk
total 8
drwxr-xr-x    2 root     root          4096 Oct  8 09:28 .
drwxr-xr-x    4 root     root          4096 Oct  8 09:28 ..
/ $ 

Checklist

• I've read the guidelines for contributing to this repository.
• I've added tests that prove my fix is effective or that my feature works.
• I've updated the documentation with the relevant information (if needed).
• I've added usage information (if the PR introduces new options)
• I've included a "before" and "after" example to the description (if the PR is a user interface change).

[afdesk]

@daanschipper thanks for the contribution!