Automatic merge from submit-queue (batch tested with PRs 44440, 44038, 44302, 44316, 43876)
Extend the gc admission plugin to check ownerReference.blockOwnerDeletion
#Extend the gc admission plugin to prevent user who doesn't have delete permission of the *owner* from changing blockOwnerDeletion field of existing ownerReferences, or adding ownerReference with blockOwnerDeletion=true.
The plugin need a RESTMapper to translate ownerRef.Kind to Resource. It should be using a dynamic one. However, as discussed in https://github.com/kubernetes/kubernetes/pull/42615, such a RESTMapper will be built after watchable discovery API is implemented, so in this PR the plugin is using the `api.Registry.RESTMapper()`, which is also [used](https://github.com/kubernetes/kubernetes/blob/master/cmd/kube-controller-manager/app/core.go#L165-L166) by the garbage collector currently.
```release-note
Extending the gc admission plugin so that a user who doesn't have delete permission of the *owner* cannot modify blockOwnerDeletion field of existing ownerReferences, or add new ownerReference with blockOwnerDeletion=true
```
cc @lavalamp
Automatic merge from submit-queue
Non global admission plugin registry
For testing the global state is a problem. This PR turns the actual registry into a struct that must be instantiated. For the beginning, we do this in `pkg/kubeapiserver/admission`. In some follow-up (where we hunt down all globals some day), we will move this into the genericapiserver.
The exported or public functions requires a doc comment to pass golint.
This commit has changes of conversion generated code. The actual doc
changes are added into a separate commit for a clean review.
Mike Danese