This commit regenerates the protobuf as per the recent generation
changes (removing erroneous imports, adding k8s.io/metrics), and
syncs the changes to client-go (which also ensures that client-go
protobuf IDL has the correct package names).
This commit is an initial pass at providing an admission API group.
The API group is required by the webhook admission controller being
developed as part of https://github.com/kubernetes/community/pull/132
and could be used more as that proposal comes to fruition.