Automatic merge from submit-queue

Add federation cluster status zone update

Hi Nikhil

Here's the cluster zone update stuff we discussed today.

What's remaining:

1. Rebase against #26308 (as soon as it merges) to expose the zones and region fields of cluster status.
2. Get hold of a cluster client via which to query nodes in the cluster. Currently we only have a DiscoveryClient, which doesn't know how to list nodes.

Any advice on the latter much appreciated.  Specifically how do I get a cluster client from a discovery client?

Q