Automatic merge from submit-queue (batch tested with PRs 66593, 66727, 66558). 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>.
Mark --pod/-p flag of kubectl exec command as deprecated
**What this PR does / why we need it**:
Marks the `--pod` (`-p` shorthand) flag of kubectl `exec` command as deprecated.
Hides the flag from the help menu, but shows a message when command is executed with this flag.
**Which issue this PR fixes**:
Fixes: https://github.com/kubernetes/kubectl/issues/104
This is a remake of PR https://github.com/kubernetes/kubernetes/pull/54629.
**Release note**:
```release-note
Flag --pod (-p shorthand) of kubectl exec command marked as deprecated
```
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