Automatic merge from submit-queue (batch tested with PRs 60737, 60739, 61080, 60968, 60951). 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 default auditing options.

- Log backend defaults to blocking mode (backwards compatability)
- Webhook backend defaults to throttled
- Fix webhook validation
- Add options test

**Which issue(s) this PR fixes**:
Fixes #60719

**Special notes for your reviewer**:
This PR is an alternative fix to https://github.com/kubernetes/kubernetes/pull/60727. If the rollback goes in first, I'll rebase this on a roll-forward.

**Release note**:
-->
```release-note
NONE
```