Skip garbage collection of objects with owner references

[stefanprodan]

Looks like #362 didn't do much, various Kubernetes controllers copy the metadata (labels and annotations) from their custom resources to generated objects. To fix this once and for all, kustomize-controller will skip pruning any object that has ownerReference.BlockOwnerDeletion=true. There is no reason why Flux should try to delete objects with BlockOwnerDeletion as Kubernetes GC should prune them.

Fix: #415
Fix: #410

Test image

To test this PR please use the following image:

ghcr.io/fluxcd/kustomize-controller:rc-a49bbf9e

To upgrade kustomize-controller on an cluster bootstrapped with flux, add the following images section to your flux-system/kustomization.yaml:

apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization
resources:
  - gotk-components.yaml
  - gotk-sync.yaml
images:
- name: ghcr.io/fluxcd/kustomize-controller
  newName: ghcr.io/fluxcd/kustomize-controller
  newTag: rc-a49bbf9e

[phillebaba]

I think that it would be good to add a small test for this if possible just because the impact seems to be very large on end users if this is ever removed in the future by accident. Other than that this looks good.

[stefanprodan]

@phillebaba I've added tests for when BlockOwnerDeletion is enabled or not.

[phillebaba]

LGTM