Automatic merge from submit-queue

add anytoken authenticator

Adds `--insecure-allow-any-token` as a flag to the API server to create an authenticator that will accept any bearer token and transform it into a user by parsing it out as `username/group1,group2,...`.

This gives an easy way to identify as a user and check permissions:
```bash
ALLOW_ANY_TOKEN=true hack/local-up-cluster.sh 
kubectl config set-cluster local-kube --server=https://localhost:6443 --insecure-skip-tls-verify=true
kubectl config set-credentials david --token=david/group1
kubectl config set-context local --cluster=local-kube --user=david
kubectl config use-context local
```

@kubernetes/sig-auth