Merge pull request #55534 from lavalamp/wh-api-fixes

Automatic merge from submit-queue. 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>.

Tighten webhook client config validation

ref kubernetes/enhancements#492

Fix up some nits left from #54889.

```release-note
NONE
```

Kubernetes-commit: 2db28383e1151e5d442b81eb73a02b3cf144615c