Automatic merge from submit-queue (batch tested with PRs 46235, 44786, 46833, 46756, 46669)
federation: Add admission controller for policy-based placement
@nikhiljindal
Here's the initial version of the scheduling policy admission controller. It's at the point where it would benefit from having another pair of eyes look at it. The main thing I'm unsure of is the serialization of Kube resources for the webhook/query call.
Release Note:
```
The federation-apiserver now supports a SchedulingPolicy admission controller that enables policy-based control over placement of federated resources.
```
Ref #39982
Handle failure cases on startup gracefully to avoid causing cascading
errors and poor initialization in other components. Initial errors from
config load cause the initializer to pause and hold requests. Return
typed errors to better communicate failures to clients.
Add code to handle two specific cases - admin wants to bypass
initialization defaulting, and mirror pods (which want to bypass
initialization because the kubelet owns their lifecycle).
Add support for creating resources that are not immediately visible to
naive clients, but must first be initialized by one or more privileged
cluster agents. These controllers can mark the object as initialized,
allowing others to see them.
Permission to override initialization defaults or modify an initializing
object is limited per resource to a virtual subresource "RESOURCE/initialize"
via RBAC.
Initialization is currently alpha.
lifecycle plugin: make use of the libraries under k8s.io/client-go/pkg/api and k8s.io/client-go/kubernetes
for the client libraries instead of k8s.io/kubernetes/client/*
move registration to AdmissionOptions
