Add support for OpenStack

[cw-kojima1003]

Summary:
This pull request allows cloud-api-adaptor(CAA) to support OpenStack-based clouds.

Background:
There is currently no provider in CAA that supports clouds built with standard OpenStack.
By implementing an OpenStack provider, we can offer secure pod execution environments in a wider range of fields.

As stated in the link below, we are focusing on implementations related to ARM CCA.
This PR provides an architecture-independent implementation.
Moving forward, we aim to execute PeerPods on OpenStack clouds that support ARM CCA.

Links:
This PR is for the purpose and related work described in the following Issue.
#2387

Task:
Adding an built-in Provider for OpenStack, referring to the following documentation.

https://github.com/confidential-containers/cloud-api-adaptor/blob/main/src/cloud-api-adaptor/docs/addnewprovider.md

• Add and initialize the OpenStack provider manager
• Add a definition for the configuration struct
• Add cloud interfaces
• Add provider interfaces
• Add additional files to modularize the code
• Add relevant unit tests
• Update entrypoint.sh and Makefile

Implemented:

• Launch Peer Pod with standard VM
• Unit tests
• Manual connectivity verification

Future implementation:

• [] Validate user-data reception on the Pod VM image
  The user-data related features are currently foundational, with validation and testing for operational integrity still pending.
• [] Create documentation for CAA deployment and Pod VM creation steps
• [] Implement end-to-end (E2E) tests (CI) for the new provider
• [] Enable CVM (Confidential Virtual Machine) launch for CCA support
• [] Other features: pause-image, VXLAN, TLS, etc

[mkulke]

I have some reservations about adding a provider without e2e tests, we cannot really make any statements about whether a provider is working or not without those.

What kind of PodVM image can be used with the provider?

[cw-kojima1003]

@mkule, thank you for your comment.

The details of the Pod VM image used are as follows:

Image source: https://quay.io/repository/confidential-containers/podvm-generic-ubuntu-amd64

For obtaining the image, we used the download-image.sh script provided by CAA.
Here is the command we used to obtain the image:

$ ./src/cloud-api-adaptor/podvm/hack/download-image.sh quay.io/confidential-containers/podvm-generic-ubuntu-amd64:v0.17.0 . -o podvm.qcow2

The obtained image was placed within the locally constructed OpenStack cluster.

I have some reservations about adding a provider without e2e tests, we cannot really make any statements about whether a provider is working or not without those.

The e2e tests are currently underway and will be committed at a later date.
We initially planned to submit the e2e tests as a separate pull request, but we can also add them to this PR.
Could you please share your opinions on this?

Finally, I have conducted PeerPod functionality tests in my local environment.
BusyBox was used to initiate the Pod.
Below, you'll find the YAML file we referenced:

apiVersion: v1
kind: Pod
metadata:
  labels:
    run: busybox
  name: busybox
spec:
  containers:
  - image: quay.io/prometheus/busybox
    name: busybox
    resources: {}
  dnsPolicy: ClusterFirst
  restartPolicy: Never
  runtimeClassName: kata-remote