move k8s.io/kubernetes/plugin/pkg/admission/initialization to
k8s.io/apiserver/pkg/admission/plugin/initialization/initialization.go;
move k8s.io/kubernetes/pkg/kubeapiserver/admission/configuration to
k8s.io/apiserver/pkg/admission/configuration.
As part of https://github.com/kubernetes/community/pull/132, thsi commit
adds a generic webhook admission controller. This plugin allows for a
completely declarative approach for filtering/matching admission requests
and for matching admission requests, calls out to an external webhook for
handling admission requests.