Automatic merge from submit-queue. 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>.
admission: wire through validating-only admission
Based on https://github.com/kubernetes/kubernetes/pull/54232.
This is important and required for beta because it affects the shape of the webhook admission plugins that are going to be produced and is needed to make sure that our existing chain continues to properly verify and protect the API objects based on their final state after webhook admission mutators run.
We discussed this in the October 11 API machinery call with @erictune and @caesarxuchao and we agreed to do this as a requirement for beta. See this part of the recording: https://www.youtube.com/watch?v=mrgDPHyr4VY#t=325 .
this is a two stage refactor when done there will be no init block in admission plugins.
Instead all plugins expose Register function which accept admission.Plugins instance.
The registration to global plugin registry happens inside Register func.
David Eads