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>

einterfaces/metrics.go

@@ -59,5 +59,6 @@ type MetricsInterface interface {
 	ObservePluginMultiHookDuration(elapsed float64)
 	ObservePluginApiDuration(pluginID, apiName string, success bool, elapsed float64)
 
+	ObserveEnabledUsers(users int64)
 	GetLoggerMetricsCollector() logr.MetricsCollector
 }