Automatic merge from submit-queue (batch tested with PRs 51824, 50476, 52451, 52009, 52237)
Plumbing the proxy dialer to the webhook admission plugin
* Fixing https://github.com/kubernetes/kubernetes/issues/49987. Plumb the `Dial` function to the `transport.Config`
* Fixing https://github.com/kubernetes/kubernetes/issues/52366. Let the webhook admission plugin sets the `TLSConfg.ServerName`.
I tested it in my gke setup. I don't have time to implement an e2e test before 1.8 release. I think it's ok to add the test later, because *i)* the change only affects the alpha webhook admission feature, and *ii)* the webhook feature is unusable without the fix. That said, it's up to my reviewer to decide.
Filed https://github.com/kubernetes/kubernetes/issues/52368 for the missing e2e test.
( The second commit is https://github.com/kubernetes/kubernetes/pull/52372, which is just a cleanup of client configuration in e2e tests. It removed a function that marshalled the client config to json and then unmarshalled it. It is a prerequisite of this PR, because this PR added the `Dial` function to the config which is not json marshallable.)
```release-note
Fixed the webhook admission plugin so that it works even if the apiserver and the nodes are in two networks (e.g., in GKE).
Fixed the webhook admission plugin so that webhook author could use the DNS name of the service as the CommonName when generating the server cert for the webhook.
Action required:
Anyone who generated server cert for admission webhooks need to regenerate the cert. Previously, when generating server cert for the admission webhook, the CN value doesn't matter. Now you must set it to the DNS name of the webhook service, i.e., `<service.Name>.<service.Namespace>.svc`.
```
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