(feature) CRD: KubernetesReleases, allow specify k8s version in cluster resource instead of vm id

[lknite]

Describe the solution you'd like

Create a CRD KubernetesReleases.

This would let us create a listing of available kubernetes versions which can be used by clusterctl, e.g.:

$ kubectl get KubernetesReleases
NAME                    Version                      Template    Date
v1.30.5-ubuntu-2204     ubuntu-2204-kube-v1.30.5     VM-106      2024-01-24
v1.30.5-ubuntu-2404     ubuntu-2404-kube-v1.30.5     VM-107      2024-01-24
v1.30.5-rockylinux-9    rockylinux-9-kube-v1.30.5    VM-108      2024-01-24

Then later, in our cluster.yaml we could specify a kubernetes version by 'name' such as 'v1.30.5' instead of by vm id. This would be good because we might want to replace a template, such as when image-builder is used to rebuild an image due to a security issue, and we wouldn't have to update all the cluster.yaml files with a new vm id... instead we could just update the KubernetesRelease resource and all the clusters would then reflect the change.

Anything else you would like to add:

• The Proxmox provider could support both, either specifying a vm-id or the kubernetes release.
• New folks can just use a vm-id, but I'd definitely be creating the KR resources and using the 'name' in the cluster yaml, and create the KR as the last step in an image-builder pipeline
• Is it possible that image-builder adds a label of some type which might make it easy for the proxmox controller to recognize an image-builder image and add it as a KubernetesRelease automatically?

[wikkyk]

I can see how this is useful. However, I don't think we'll be able to fit it into 0.6.0/v1alpha2.