Automatic merge from submit-queue. If you want to cherry-pick this change to another branch, please follow the instructions here: https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md.

Refactor admission webhook client code to a apiserver/pkg/util package

As part of #67006 This refactoring enable us to share code between admission webhooks and CRD conversion webhooks.

@deads2k @lavalamp @sttts @kubernetes/sig-api-machinery-misc