Feature Request: Vitess provide a vtgate queries metric by tablet type

[jwangace]

Feature Description

Vtgate has metrics:

vtgate_queries_processed
vtgate_queries_routed

But those metrics does not distinguish queries by tablet type(RRIMARY, REPLICA), it would be great to have break down metrics, for example:

vtgate_queries_processed_primary
vtgate_queries_processed_replica
vtgate_queries_routed_primary
vtgate_queries_routed_replica

Use Case(s)

This will provide user better ideas of queries to which type of tables are sent.

[mattlord]

/cc @vitessio/query-serving

[deepthi]

If we decide to do this, we should add a dimension to vtgate_queries_processed to represent tablet_type. We would not want to duplicate the metric for every serving tablet type of which we have more than two.