Added to_callsign to atak GeoChat

meshtastic/atak.options

@@ -3,4 +3,5 @@
 *Status.battery int_size:8
 *PLI.course int_size:16
 *GeoChat.message max_size:200
-*GeoChat.to max_size:120
+*GeoChat.to max_size:120
+*GeoChat.to_callsign max_size:120

meshtastic/atak.proto

@@ -56,6 +56,11 @@ message GeoChat {
    * Uid recipient of the message
    */
   optional string to = 2;
+
+  /*
+   * Callsign of the recipient for the message
+   */
+  optional string to_callsign = 2;
 }
 
 /*