[multistage] Missing Metrics like QPS

There were some metrics added for multistage queries in: https://github.com/apache/pinot/commit/70c4c5b8019b3c3b71865bde71e4899c3659082e

But there's still some work to be done. Even for some of the existing metrics like QPS, we are emitting those at table-level, so a given query would get counted for each table that is present in it, leading to an overestimation of QPS.

Creating this ticket for tracking and gathering any other requirements. We can follow-up with some quick PRs later.

- [ ] Emit Broker Response with Num Groups Limit reached metric

cc: @walterddr @vvivekiyer

Start by reviewing commit 70c4c5b8019b3c3b71865bde71e4899c3659082e and the existing multistage metric emission paths. Determine the remaining metric requirements, including the Broker Response metric for the Num Groups Limit, and verify that QPS is not counted once per table.

Written by the indexing model from the issue text.