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

go.mod

@@ -61,7 +61,7 @@ require (
 	github.com/mattermost/gorp v1.6.2-0.20200624165429-2595d5e54111
 	github.com/mattermost/gosaml2 v0.3.2
 	github.com/mattermost/ldap v0.0.0-20191128190019-9f62ba4b8d4d
-	github.com/mattermost/logr v1.0.5
+	github.com/mattermost/logr v1.0.9
 	github.com/mattermost/rsc v0.0.0-20160330161541-bbaefb05eaa0
 	github.com/mattermost/viper v1.0.4
 	github.com/mattn/go-colorable v0.1.7 // indirect