Replace deprecated kustomize config patchesStrategicMerge

[AndiDog]

Indirect part of giantswarm/roadmap#2217 since I have to develop CAPI changes and test them.

This PR switches to using our own fork and images of cluster-api (see new main branch in https://github.com/giantswarm/cluster-api). It's consistent to how we manage our CAPA fork – from which I also took parts of the newer "generate patches" script. Once merged, we can turn off mirroring upstream images (retagger). (will move the fork part into another PR)

Since kustomize does not support multiple patches in one file anymore (kubernetes-sigs/kustomize#5049), I split those into several files. Hence the large diff.

Checklist

• Update changelog in CHANGELOG.md.

[nprokopic]

Since kustomize does not support multiple patches in one file anymore (kubernetes-sigs/kustomize#5049), I split those into several files. Hence the large diff.

Would it be possible to have this and the switch to fork in separate PRs? Both are non-trivial and important changes (one to structure of the repo, another to what is the source of truth for generating manifests here), so IMO we should not mix those in a single PR, if we can have it done in two steps.

In addition to switching to fork, and separating kustomize patches to separate files, is there some other source of / reason for some of the changes?

[AndiDog]

In addition to switching to fork, and separating kustomize patches to separate files, is there some other source of / reason for some of the changes?

Apart from pointing to the fork, which I have now removed from this PR, all changes are about getting the kustomize build to work with the latest version (e.g. splitting patches).

[AndiDog]

@nprokopic any more concerns?

[nprokopic]

any more concerns?

Nope.

Thanks a lot for working on this! 🥳 🙇