Merge /v1/clusters and /v1/tfcontroller endpoints

[foot]

What changed?

• Unify CAPITemplate / GitopsTemplate endpoints
  • POST /v1/tfcontroller now just calls /v1/clusters
  • /v1/clusters can now be called with templateKind=GitopsTemplate too
• Right now CAPITemplates have some extra helpers during rendering
  • add-common-bases: includes a kustomization file that will apply all files in ./clusters/bases to the new cluster
  • inject-prune-annotation: proper cluster deletion of clusters with flux
  • CAPITemplates have both these transforms on by default
  • GitopsTemplates can enable with an annotation to help users transition to GitopsTemplate.

Behaviour changes

• Preview now includes the common-bases if its been added
• /v1/tfcontroller now includes the namespace in the path it writes out.
  • old: ./clusters/management/clusters/rds.yaml
  • new: ./clusters/management/clusters/default/rds.yaml

Closes #969
Closes #1062

Why was this change made?

• So we have a single endpoint for rendering templates.
  • Render behaviour can be tweaked via annotations rather than using different endpoints.
  • We don't have to maintain two endpoints.
  • GitopsTemplates/CAPITemplates already use the same preview endpoint, now they use the same create-pr endpoint too.
• We can remove the /v1/tfcontroller endpoint in the future.

How did you validate the change?

Unit tests

[bigkevmcd]

I'm ok with this.

I have concerns around the defaulting of the template kind, and around the annotation for pruning, it feels like an odd thing (why would you add it there, but not on the resources that follow?) but it's cheap to maintain and do, so I don't think this is a blocker.

[foot]

around the annotation for pruning, it feels like an odd thing (why would you add it there, but not on the resources that follow?)

Yeah, it gets added to everything except capi.Cluster / weave.GitopsCluster. So it will get applied to any other kustomizations/helmreleases you might add too which is no good, feels a bit broken. We could try and improve it so it gets applied to everything in apiVersion: /.*cluster.x-k8s.io.*/ thats not a Cluster.

It is a bit of a funky/"magic" feature, but its sort of nice UX too, lets the user write templates without having to understand the subtler issues around managing CAPI with flux. How does argo handle this.. 👀