Add metrics for mobile versions snapshots (#28191)

* Add metrics for mobile versions snapshots

* Add notifications disabled and fix lint

* Address feedback

* Verify all references to JobTypeActiveUsers

* Fix typos

* Improve platform values

* Add test and MySQL support

server/einterfaces/metrics.go

@@ -118,4 +118,6 @@ type MetricsInterface interface {
 	ObserveMobileClientLoadDuration(platform string, elapsed float64)
 	ObserveMobileClientChannelSwitchDuration(platform string, elapsed float64)
 	ObserveMobileClientTeamSwitchDuration(platform string, elapsed float64)
+	ClearMobileClientSessionMetadata()
+	ObserveMobileClientSessionMetadata(version string, platform string, value float64, notificationDisabled string)
 }