feat: support configurable game server address and port

* Launch game servers in headless mode
* Add configurable game address and port to GameData
* Pass dynamically assigned server ports to clients
* Update lobby defaults for `0.0.0.0:8080`
* Refactor server command-line argument handling

server.gd

@@ -22,6 +22,8 @@ func _ready() -> void:
 	for arg in OS.get_cmdline_user_args():
 		if "name_" in arg:
 			name_(arg)
+		elif "server_" in arg:
+			server_(arg)
 
 		match arg:
 			"server":
@@ -36,6 +38,16 @@ func name_(arg: String) -> void:
 	var game_name = arg.split("_")[-1]
 	self.name     = game_name
 
+func server_(arg: String) -> void:
+	var host_port = float(arg.split("_")[-1])
+
+	Globals.game_state.set_game_scene(
+		"res://scenes/screens/lobby_screen/lobby.tscn"
+	)
+
+	$scene/lobby_screen.find_child("host_port_range", true, false).set_value_no_signal(host_port)
+	$scene/lobby_screen.find_child("host_start_bttn", true, false).emit_signal("pressed")
+
 func server(_arg: String) -> void:
 	Globals.game_state.set_game_scene(
 		"res://scenes/screens/lobby_screen/lobby.tscn"