[DocDB] in yb-master /tablet-servers view summarize read-replica and primary cluster info separately

Jira Link: DB-1322 Sample screenshot from the http://yb-master:7000/tablet-servers view of a Yugabyte universe with a primary cluster + read-replica cluster:

As you can see, the Tablet-Peers by Availability Zone section simply summarizes by "cloud+region+zone". But if the cloud/region/zone names are the same for the primary cluster nodes and read-replica cluster nodes (as in this case) -- then the summary view isn't as useful as it could be. Would be nice to have two summary sections for this -- one for the primary cluster and one for the read-replica cluster.

cc: @bmatican , @rahuldesirazu .