Automatic merge from submit-queue

Add CoreDNS as Federation DNS provider

This PR contains following
1. DNS provider implementation for CoreDNS with etcd as backend
2. Script for optionally deploying CoreDNS in federation control plane

Still to do:
1. HA for CoreDNS service need to be handled, would be taken up in subsequent PR
2. Need to configure CoreDNS as fallback DNS to in-cluster KubeDNS(Manual Step). Need to consider automation.

Request for review: @quinton-hoole @madhusudancs @nikhiljindal @kshafiee @deepak-vij
cc @kubernetes/sig-cluster-federation