✨ Add registry_mirrors feature

[Nils98Ar]

What this PR does / why we need it:

Add ClusterClass variable registry_mirrors to openstack scs ClusterStack for configuring registry mirrors in containerd.

Example value:

[ { hostname_upstream: "docker.io", url_upstream: "https://registry-1.docker.io", url_mirror: "https://registry.foo.tld/v2/foo", cert_mirror: "" }, { hostname_upstream: "gcr.io", url_upstream: "https://gcr.io", url_mirror: "https://registry.bar.tld/v2/foo", cert_mirror: "" } ]

TODOs:

• include documentation

[garloff]

I like this.
Can we get reviews? @jschoone ? @matofeder ?

[garloff]

Needs rebase.

[garloff]

This was not pulled into scs2, but we could add it (with the right default) in a non breaking way.
Feedack?

[jschoone]

This was not pulled into scs2, but we could add it (with the right default) in a non breaking way. Feedack?

Yes, but I see some challenges here which seem to be a string of problems. First the patch requires containerd. This is not optimal, but also not too bad because because the images we used to use have containerd. But those images are no longer available as they were before. I think we should provide them ourselves now. Either we prebuild them with image-builder or diskimage-builder or we just install the packages as we did before in our first ClusterClass tests. Actually I prefer the latter, even it's not as reproducible, but since we missed the immutability anyway we won't lose much value. Additionally we can make better use of the builtin variables.

Back to this PR: we can then choose which container runtime to install in the preKubeadmCommands to make the config work.

[Nils98Ar]

@jschoone Is it already the case that new images are no longer provided by OSISM? E.g. I am missing the ubuntu-2404-kube-v1.33.6 image for the scs2 v3 ClusterStack.

[jschoone]

Ok @Nils98Ar showed me it works now with the new location of the images. Yesterday it didn't when I wanted to provide the ORC image resource. That saves time.
Those images have containerd so they will work with that patch.

[jschoone]

Add a PR regarding images: #245