Track replication started vs replication failed refs Add metrics to track number of refs for which fetch operation have started/completed/failed. New metric names: * plugins_pull_replication_fetch_refs_started_total * plugins_pull_replication_fetch_refs_failed_total * plugins_pull_replication_fetch_refs_completed_total Bug: Issue 290254822 Change-Id: I20140b25064b034375ae6af19086bdff3717a770