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.sum

@@ -425,8 +425,10 @@ github.com/mattermost/gosaml2 v0.3.2 h1:kq2dY5qUe6fPPHra171GVlgo+ycBsEog0gZMetxL
 github.com/mattermost/gosaml2 v0.3.2/go.mod h1:Z429EIOiEi9kbq6yHoApfzlcXpa6dzRDc6pO+Vy2Ksk=
 github.com/mattermost/ldap v0.0.0-20191128190019-9f62ba4b8d4d h1:2DV7VIlEv6J5R5o6tUcb3ZMKJYeeZuWZL7Rv1m23TgQ=
 github.com/mattermost/ldap v0.0.0-20191128190019-9f62ba4b8d4d/go.mod h1:HLbgMEI5K131jpxGazJ97AxfPDt31osq36YS1oxFQPQ=
-github.com/mattermost/logr v1.0.5 h1:TST38xROPguNh8o90BfDHpp1bz6HfTdFYX5Btw/oLwM=
-github.com/mattermost/logr v1.0.5/go.mod h1:YzldchiJXgF789YNDFGXVoCHTQOTrCKwWft9Fwev1iI=
+github.com/mattermost/logr v1.0.8 h1:Frkfo+FXGOShiSN3pljflqEMS9AKGySdTHHu36MYPXU=
+github.com/mattermost/logr v1.0.8/go.mod h1:Mt4DPu1NXMe6JxPdwCC0XBoxXmN9eXOIRPoZarU2PXs=
+github.com/mattermost/logr v1.0.9 h1:jw6f6CjPC2YfPqzpGVM/vCGuqKLJdVS400ZRTFtEQwQ=
+github.com/mattermost/logr v1.0.9/go.mod h1:Mt4DPu1NXMe6JxPdwCC0XBoxXmN9eXOIRPoZarU2PXs=
 github.com/mattermost/rsc v0.0.0-20160330161541-bbaefb05eaa0 h1:G9tL6JXRBMzjuD1kkBtcnd42kUiT6QDwxfFYu7adM6o=
 github.com/mattermost/rsc v0.0.0-20160330161541-bbaefb05eaa0/go.mod h1:nV5bfVpT//+B1RPD2JvRnxbkLmJEYXmRaaVl15fsXjs=
 github.com/mattermost/viper v1.0.4 h1:cMYOz4PhguscGSPxrSokUtib5HrG4gCpiUh27wyA3d0=