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/enterprise/metrics/metrics.go

@@ -215,6 +215,7 @@ type MetricsInterfaceImpl struct {
 	MobileClientLoadDuration          *prometheus.HistogramVec
 	MobileClientChannelSwitchDuration *prometheus.HistogramVec
 	MobileClientTeamSwitchDuration    *prometheus.HistogramVec
+	MobileClientSessionMetadataGauge  *prometheus.GaugeVec
 }
 
 func init() {
@@ -1335,6 +1336,17 @@ func New(ps *platform.PlatformService, driver, dataSource string) *MetricsInterf
 	)
 	m.Registry.MustRegister(m.MobileClientTeamSwitchDuration)
 
+	m.MobileClientSessionMetadataGauge = prometheus.NewGaugeVec(
+		prometheus.GaugeOpts{
+			Namespace: MetricsNamespace,
+			Subsystem: MetricsSubsystemClientsMobileApp,
+			Name:      "mobile_session_metadata",
+			Help:      "The number of mobile sessions in each version, platform and whether they have the notifications disabled",
+		},
+		[]string{"version", "platform", "notifications_disabled"},
+	)
+	m.Registry.MustRegister(m.MobileClientSessionMetadataGauge)
+
 	return m
 }
 
@@ -1850,6 +1862,14 @@ func (mi *MetricsInterfaceImpl) ObserveMobileClientTeamSwitchDuration(platform s
 	mi.MobileClientTeamSwitchDuration.With(prometheus.Labels{"platform": platform}).Observe(elapsed)
 }
 
+func (mi *MetricsInterfaceImpl) ObserveMobileClientSessionMetadata(version string, platform string, value float64, notificationDisabled string) {
+	mi.MobileClientSessionMetadataGauge.With(prometheus.Labels{"version": version, "platform": platform, "notifications_disabled": notificationDisabled}).Set(value)
+}
+
+func (mi *MetricsInterfaceImpl) ClearMobileClientSessionMetadata() {
+	mi.MobileClientSessionMetadataGauge.Reset()
+}
+
 func extractDBCluster(driver, connectionString string) (string, error) {
 	host, err := extractHost(driver, connectionString)
 	if err != nil {