feat(multiplayer): add Steam transport foundation

Game/scripts/enet_transport.gd

@@ -0,0 +1,21 @@
+class_name EnetTransport
+extends NetTransport
+
+func transport_id() -> String:
+	return "enet"
+
+
+func is_available() -> bool:
+	return true
+
+
+func create_server(port: int, max_clients: int) -> Dictionary:
+	var peer := ENetMultiplayerPeer.new()
+	var err := peer.create_server(port, max_clients)
+	return {"error": err, "peer": peer if err == OK else null, "reason": error_string(err)}
+
+
+func create_client(address: String, port: int) -> Dictionary:
+	var peer := ENetMultiplayerPeer.new()
+	var err := peer.create_client(address, port)
+	return {"error": err, "peer": peer if err == OK else null, "reason": error_string(err)}