Include forwarding version in modern forwarding

This is currently version 1.

proxy/src/main/java/com/velocitypowered/proxy/connection/VelocityConstants.java

@@ -6,5 +6,5 @@ public class VelocityConstants {
     }
 
     public static final String VELOCITY_IP_FORWARDING_CHANNEL = "velocity:player_info";
-
+    public static final int FORWARDING_VERSION = 1;
 }

proxy/src/main/java/com/velocitypowered/proxy/connection/backend/LoginSessionHandler.java

@@ -123,6 +123,7 @@ public class LoginSessionHandler implements MinecraftSessionHandler {
         ByteBuf dataToForward = Unpooled.buffer();
         ByteBuf finalData = Unpooled.buffer();
         try {
+            ProtocolUtils.writeVarInt(dataToForward, VelocityConstants.FORWARDING_VERSION);
             ProtocolUtils.writeString(dataToForward, address);
             ProtocolUtils.writeUuid(dataToForward, profile.idAsUuid());
             ProtocolUtils.writeString(dataToForward, profile.getName());