MM-27199 - Add metrics to MM server for total enabled user count (#15116)

* Add metrics to MM server for total enabled user count and include installation ID from a new env var

* diagnostics context

Co-authored-by: Mattermod <mattermod@users.noreply.github.com>

app/enterprise.go

@@ -90,6 +90,12 @@ func RegisterJobsBleveIndexerInterface(f func(*Server) tjobs.IndexerJobInterface
 	jobsBleveIndexerInterface = f
 }
 
+var jobsActiveUsersInterface func(*App) tjobs.ActiveUsersJobInterface
+
+func RegisterJobsActiveUsersInterface(f func(*App) tjobs.ActiveUsersJobInterface) {
+	jobsActiveUsersInterface = f
+}
+
 var jobsExpiryNotifyInterface func(*App) tjobs.ExpiryNotifyJobInterface
 
 func RegisterJobsExpiryNotifyJobInterface(f func(*App) tjobs.ExpiryNotifyJobInterface) {