Merge pull request #54165 from caesarxuchao/webhook-e2e-test

Automatic merge from submit-queue (batch tested with PRs 54165, 53909). 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>.

Adding an e2e test for admission webhook

Part of kubernetes/enhancements#492

The purpose of this test is making sure the webhooks get called, and the apiserver can communicate with the webhook.

We will expand the test cover more webhook features in followups.

The webhook used in the test rejects pods with container names "webhook-disallow". Will upload the source code of the example in a follow up PR.

Kubernetes-commit: 444d0c11153647d45b899b25a5dbbd3a5ea4a123