🐛 remove metadata.creationTimestamp when generating CRDs, RBAC, and webhooks

[joelanford]

Closes #402

This issue has been open for awhile, but seemingly not that big of a deal until kustomize v5 was released with a bug that converts null to "null". And that causes manifests to fail to apply.

kubernetes-sigs/kustomize#5031

We can stem the tide in controller-tools by removing creationTimestamp: null just before writing the generated manifests. This was always unsightly/superfluous anyways.

[camilamacedo86]

/lgtm

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: camilamacedo86, joelanford

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[joelanford]

/cherry-pick release-0.11

[k8s-infra-cherrypick-robot]

@joelanford: #800 failed to apply on top of branch "release-0.11":

Applying: remove metadata.creationTimestamp when generating CRDs, RBAC, and webhooks
Using index info to reconstruct a base tree...
M	pkg/crd/gen.go
M	pkg/genall/genall.go
M	pkg/rbac/parser.go
M	pkg/webhook/parser.go
A	pkg/webhook/testdata/valid-ordered/manifests.yaml
Falling back to patching base and 3-way merge...
CONFLICT (modify/delete): pkg/webhook/testdata/valid-ordered/manifests.yaml deleted in HEAD and modified in remove metadata.creationTimestamp when generating CRDs, RBAC, and webhooks. Version remove metadata.creationTimestamp when generating CRDs, RBAC, and webhooks of pkg/webhook/testdata/valid-ordered/manifests.yaml left in tree.
Auto-merging pkg/webhook/parser.go
CONFLICT (content): Merge conflict in pkg/webhook/parser.go
Auto-merging pkg/rbac/parser.go
CONFLICT (content): Merge conflict in pkg/rbac/parser.go
Auto-merging pkg/genall/genall.go
Auto-merging pkg/crd/gen.go
CONFLICT (content): Merge conflict in pkg/crd/gen.go
error: Failed to merge in the changes.
hint: Use 'git am --show-current-patch=diff' to see the failed patch
Patch failed at 0001 remove metadata.creationTimestamp when generating CRDs, RBAC, and webhooks
When you have resolved this problem, run "git am --continue".
If you prefer to skip this patch, run "git am --skip" instead.
To restore the original branch and stop patching, run "git am --abort".

In response to this:

/cherry-pick release-0.11

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