Merge pull request #45919 from ericchiang/audit-webhook-backend

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

hack/.linted_packages

@@ -359,6 +359,7 @@ staging/src/k8s.io/apiserver/pkg/storage/storagebackend/factory
 staging/src/k8s.io/apiserver/pkg/storage/value/encrypt/aes
 staging/src/k8s.io/apiserver/pkg/util/flushwriter
 staging/src/k8s.io/apiserver/pkg/util/logs
+staging/src/k8s.io/apiserver/plugin/pkg/audit/webhook
 staging/src/k8s.io/apiserver/plugin/pkg/authenticator
 staging/src/k8s.io/apiserver/plugin/pkg/authenticator/password
 staging/src/k8s.io/apiserver/plugin/pkg/authenticator/password/allow

hack/verify-flags/known-flags.txt

@@ -46,6 +46,8 @@ audit-log-maxage
 audit-log-maxbackup
 audit-log-maxsize
 audit-log-path
+audit-webhook-config-file
+audit-webhook-mode
 authentication-kubeconfig
 authentication-token-webhook
 authentication-token-webhook-cache-ttl