Automatic merge from submit-queue (batch tested with PRs 67298, 67518, 67635, 67673). If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.

Fix unstructured metadata accessors to respect omitempty semantics

Fixes #67541
Fixes #48211 
Fixes #49075
Follow up of #67562

`ObjectMeta` has fields with `omitempty` json tags. This means that when the fields have zero values, they should not be persisted in the object.

Before this PR, some of the metadata accessors for unstructured objects did not respect these semantics i.e they would persist a field even if it had a zero value.

This PR updates the accessors so that the field is removed from the unstructured object map if it contains a zero value.

/sig api-machinery
/kind bug
/area custom-resources
/cc sttts liggitt yue9944882 roycaihw 
/assign sttts liggitt 

**Release note**:

```release-note
NONE
```