MM-22786 enterprise metrics for logging (#15313)

Adds metrics for logging engine which are collected by Prometheus.
- current queue level(s)
- rate of logging records emitted
- rate of logging errors

vendor/modules.txt

@@ -282,7 +282,7 @@ github.com/mattermost/gosaml2/uuid
 # github.com/mattermost/ldap v0.0.0-20191128190019-9f62ba4b8d4d
 ## explicit
 github.com/mattermost/ldap
-# github.com/mattermost/logr v1.0.5
+# github.com/mattermost/logr v1.0.9
 ## explicit
 github.com/mattermost/logr
 github.com/mattermost/logr/format