Add mobile metrics (#27045)

* Add mobile metrics

* Fix mocks

* Add tests

* Fix lint

* Address feedback

* Fix lint

* Fix test

* Fix CI

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Co-authored-by: Mattermost Build <build@mattermost.com>

server/public/model/metrics.go

@@ -26,6 +26,10 @@ const (
 	ClientRHSLoadDuration           MetricType = "rhs_load"
 	ClientGlobalThreadsLoadDuration MetricType = "global_threads_load"
 
+	MobileClientLoadDuration          MetricType = "mobile_load"
+	MobileClientChannelSwitchDuration MetricType = "mobile_channel_switch"
+	MobileClientTeamSwitchDuration    MetricType = "mobile_team_switch"
+
 	performanceReportTTLMilliseconds = 300 * 1000 // 300 seconds/5 minutes
 )