Automatic merge from submit-queue
apiserver: add a webhook implementation of the audit backend
This builds off of #45315 and is intended to implement an interfaced defined in #45766.
TODO:
- [x] Rebase on top of API types PR.
- [x] Rebase on top of API types updates (#46065)
- [x] Rebase on top of feature flag (#46009)
- [x] Rebase on top of audit instrumentation.
- [x] Hook up API server flag or register plugin (depending on #45766)
Features issue https://github.com/kubernetes/features/issues/22
Design proposal https://github.com/kubernetes/community/blob/master/contributors/design-proposals/auditing.md
```release-notes
Webhook added to the API server which omits structured audit log events.
```
/cc @soltysh @timstclair @soltysh @deads2k
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