feat(dbus): Add initial D-Bus middleware implementation

Introduce a D-Bus middleware module for revpi_middleware, including an
interface definition and a `BusProvider` class to handle D-Bus
communication. This forms the foundation for middleware interactions
using D-Bus.

src/revpi_middleware/dbus_middleware1/__init__.py

@@ -0,0 +1,8 @@
+# -*- coding: utf-8 -*-
+# SPDX-FileCopyrightText: 2025 KUNBUS GmbH
+# SPDX-License-Identifier: GPL-2.0-or-later
+"""D-Bus middleware version 1 of revpi_middleware."""
+from ..__about__ import __author__, __copyright__, __license__, __version__
+
+REVPI_DBUS_NAME = "com.revolutionpi.middleware1"
+REVPI_DBUS_BASE_PATH = "/com/revolutionpi/middleware1"