Feature: Allow setting a different port in the motd (#4293)

* Allow changing the broadcasted port using a system property. This may be needed if the port Geyser runs on & the port Bedrock players connect on do not match - e.g. due to port forwarding/different routing.

* initial stab at making the broadcast port an (unsafe) config option

* Automatically set broadcast port to be the bind port unless manually overridden

* Warn about broadcast port mismatch

* Use 0 instead of -1 as indicator to broadcast the port geyser is running on

api/src/main/java/org/geysermc/geyser/api/network/BedrockListener.java

@@ -50,6 +50,14 @@ public interface BedrockListener {
      */
     int port();
 
+    /**
+     * Gets the broadcast port that's sent to Bedrock clients with the motd.
+     * This is the port that Bedrock clients will connect with. It usually does not differ from the listening port.
+     *
+     * @return the broadcast port
+     */
+    int broadcastPort();
+
     /**
      * Gets the primary MOTD shown to Bedrock players if a ping passthrough setting is not enabled.
      * <p>