MM-58092 Add feature flag and setting for client performance metrics (#26942)

* MM-58092 Add feature flag and setting for client performance metrics

* Fix incorrect field name

server/public/model/feature_flags.go

@@ -55,6 +55,8 @@ type FeatureFlags struct {
 	WebSocketEventScope bool
 
 	NotificationMonitoring bool
+
+	ClientMetrics bool
 }
 
 func (f *FeatureFlags) SetDefaults() {
@@ -78,6 +80,7 @@ func (f *FeatureFlags) SetDefaults() {
 	f.ChannelBookmarks = false
 	f.WebSocketEventScope = false
 	f.NotificationMonitoring = true
+	f.ClientMetrics = false
 }
 
 // ToMap returns the feature flags as a map[string]string