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Prevent webhooks from affecting admission requests for WebhookConfiguration objects

**What this PR does / why we need it**:
As it stands now webhooks can be added to the system which make it impossible for a user to remove that webhook, or two webhooks could be registered which make it impossible to remove each other.

The first commit of this will add a test to make sure webhook deletion is never blocked by a webhook. This test will fail until the second commit is added which will prevent webhooks from affecting admission requests for ValidatingWebhookConfiguration and MutatingWebhookConfiguration objects in the admissionregistration.k8s.io group

- [x] Test that webhook deletion is never blocked by a webhook ([test fails before second commit](https://k8s-gubernator.appspot.com/build/kubernetes-jenkins/pr-logs/pull/59840/pull-kubernetes-e2e-gce/23731/))
- [x] Prevent webhooks from being called on admission requests for [Validating|Mutating]WebhookConfiguration objects
- [x] Document this new behavior maybe in another PR

**Which issue(s) this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close the issue(s) when PR gets merged)*:
Part of fixing #59124 (Verifies that it can remove the broken webhook.)

**Release note**:
```release-note
ValidatingWebhooks and MutatingWebhooks will not be called on admission requests for ValidatingWebhookConfiguration and MutatingWebhookConfiguration objects in the admissionregistration.k8s.io group
```