Allow correlating gRPC calls from indexer to Gitaly
When the ES-indexer performs RPCs to Gitaly, there's no way to tell through Prometheus how many, and what their latencies are. This is important to spot inconsitencies, and detect N + 1 issues.
From both the client side, and the Gitaly side Prometheus metrics should be added to correlate gRPC traffic with their source.
Edited by Zeger-Jan van de Weg