Add priority for new critical alert feature

meshtastic/mesh.proto

@@ -1095,6 +1095,11 @@ message MeshPacket {
      */ 
     HIGH = 100;
 
+    /*
+     * Higher priority alert message used for critical messages which take priority over other reliable packets.
+     */ 
+    ALERT = 110;
+
     /*
      * Ack/naks are sent with very high priority to ensure that retransmission
      * stops as soon as possible