expose top-level ops count in http://<master>:7000/tablet-servers view

[kmuthukk]

Jira Link: DB-2184
Today, in the master UI's /tablet-servers view, the read/write IOPS shown correspond to the internal TServer/DocDB level read/write operations. This may not correspond 1-to-1 to the top-level operations coming via YCQL/YEDIS/YSQL protocols.

For example, an update to a table with secondary index would typically result in 3 underlying operations at three different TServers (1 update going to the TServer which holds the row, 1 delete to the TServer holding the old index entry, and 1 insert to the TServer for the new index entry).

The /tablet-servers UI today shows the latter count (i.e. 3). We should also add counters in this view for the top-level operation (e.g., for the earlier example, that would be 1 YCQL/YSQL Update operation).