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update apps/v1 types.go comments for controller spec selector fields
**What this PR does / why we need it**:
This PR updates apps/v1 types.go comments (including removal of `optional` tag) for controller spec selector fields.
**Which issue(s) this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close the issue(s) when PR gets merged)*:
xref #50808
**Release note**:
```release-note
NONE
```
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