feat(cli): Add D-Bus helper functions for CLI commands.

This introduces `simple_call`, a utility function to interact with D-Bus
interfaces within the RevPi system. It facilitates method invocation on
specific interfaces and paths, improving modularity and code reuse in
middleware operations.

src/revpi_middleware/cli_commands/__init__.py

@@ -0,0 +1,5 @@
+# -*- coding: utf-8 -*-
+# SPDX-FileCopyrightText: 2025 KUNBUS GmbH
+# SPDX-License-Identifier: GPL-2.0-or-later
+"""CLI commands to control revpi_middleware."""
+from ..__about__ import __author__, __copyright__, __license__, __version__