kv: add metrics measuring request evaluation count per request type on each Store #50660
Description
#46747 is adding metrics for each request type sent by the DistSender, which already had other metrics counting entire batches sent, partial batches sent, etc. It turns out that we have no corresponding metrics on the server-side of these RPCs. That makes it difficult to spot hotspots in the cluster in cases where all nodes are sending to the same destination node. We should add such metrics.
Jira issue: CRDB-4103