Import of provisioners from private OCI registry/image

[7h3-3mp7y-m4n]

Description

Added the docker login support

as mentioned here: https://github.com/oras-project/oras-go/blob/main/example_test.go#L106
#60

What does this PR do?

This PR supports dynamic login which uses $DOCKER_CONFIG/config.json for login..

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• New chore (expected functionality to be implemented)

Checklist:

• My change requires a change to the documentation.
  • I have updated the documentation accordingly.
• I've signed off with an email address that matches the commit author.

[7h3-3mp7y-m4n]

I've tested it with my own local function, which goes like this

func ExampleGetFile_privateOCI() {
	testUrl := "oci://localhost:5001/provisioners/hello:v1#hello.yaml"
	buff, err := GetFile(context.Background(), testUrl)
	if err != nil {
		fmt.Println("failed to pull OCI image:", err)
		return
	}
	fmt.Println(len(buff) > 0)
	// Output:
	// true
}

It passes for me when I use the oras guide https://oras.land/docs/compatible_oci_registries#cncf-distribution
If we need to add a stable test, then we need to recreate this, and also, I believe, by adding helper docker commands and pushing and pulling it, so that will be hectic. But if we are planning for this, then I would like to work on that, too!