Include websocket users metric (#14020)

This commit adds new metrics to know the number of registered users
we have in every WebSocket broadcasts hub

app/web_hub.go

@@ -161,6 +161,9 @@ func (a *App) GetHubForUserId(userId string) *Hub {
 func (a *App) HubRegister(webConn *WebConn) {
 	hub := a.GetHubForUserId(webConn.UserId)
 	if hub != nil {
+		if metrics := a.Metrics(); metrics != nil {
+			metrics.IncrementWebSocketBroadcastUsersRegistered(strconv.Itoa(hub.connectionIndex), 1)
+		}
 		hub.Register(webConn)
 	}
 }
@@ -168,6 +171,9 @@ func (a *App) HubRegister(webConn *WebConn) {
 func (a *App) HubUnregister(webConn *WebConn) {
 	hub := a.GetHubForUserId(webConn.UserId)
 	if hub != nil {
+		if metrics := a.Metrics(); metrics != nil {
+			metrics.DecrementWebSocketBroadcastUsersRegistered(strconv.Itoa(hub.connectionIndex), 1)
+		}
 		hub.Unregister(webConn)
 	}
 }