Automatic merge from submit-queue

Allow secure access to apiserver from Admission Controllers

* Allow options.InsecurePort to be set to 0 to switch off insecure access
* In NewSelfClient, Set the TLSClientConfig to the cert and key files
  if InsecurePort is switched off
* Mint a bearer token that allows the client(s) created in NewSelfClient
  to talk to the api server
* Add a new authenticator that checks for this specific bearer token

Fixes #13598