Add alert app portnum

meshtastic/portnums.proto

@@ -105,6 +105,11 @@ enum PortNum {
    */
   DETECTION_SENSOR_APP = 10;
 
+  /*
+   * Same as Text Message but used for critical alerts.
+   */
+  ALERT_APP = 11;
+
   /*
    * Provides a 'ping' service that replies to any packet it receives.
    * Also serves as a small example module.