Instruct helm to keep workload groups around on deletion

[liamawhite]

Every other CRD has this annotation set so add it to WorkloadGroup.

Noticed this as I was root causing why this CRD was missing from one of our clusters.

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[howardjohn]

Nice find 👍

[istio-testing]

In response to a cherrypick label: new pull request created: #3593

[istio-testing]

In response to a cherrypick label: #3592 failed to apply on top of branch "release-1.26":

Applying: Instruct helm to keep workload groups around on deletion
Using index info to reconstruct a base tree...
M	kubernetes/customresourcedefinitions.gen.yaml
M	networking/v1/workload_group_alias.gen.go
M	networking/v1alpha3/workload_group.pb.go
M	networking/v1alpha3/workload_group.proto
M	networking/v1beta1/workload_group_alias.gen.go
Falling back to patching base and 3-way merge...
Auto-merging networking/v1beta1/workload_group_alias.gen.go
CONFLICT (content): Merge conflict in networking/v1beta1/workload_group_alias.gen.go
Auto-merging networking/v1alpha3/workload_group.proto
CONFLICT (content): Merge conflict in networking/v1alpha3/workload_group.proto
Auto-merging networking/v1alpha3/workload_group.pb.go
CONFLICT (content): Merge conflict in networking/v1alpha3/workload_group.pb.go
Auto-merging networking/v1/workload_group_alias.gen.go
CONFLICT (content): Merge conflict in networking/v1/workload_group_alias.gen.go
Auto-merging kubernetes/customresourcedefinitions.gen.yaml
error: Failed to merge in the changes.
hint: Use 'git am --show-current-patch=diff' to see the failed patch
hint: When you have resolved this problem, run "git am --continue".
hint: If you prefer to skip this patch, run "git am --skip" instead.
hint: To restore the original branch and stop patching, run "git am --abort".
hint: Disable this message with "git config advice.mergeConflict false"
Patch failed at 0001 Instruct helm to keep workload groups around on deletion

[istio-testing]

In response to a cherrypick label: new issue created for failed cherrypick: #3594

[istio-testing]

In response to a cherrypick label: new pull request created: #3595