feat: Add python base project files

These files create a callable Python package and manage the version
number of the complete project in the __about__.py file only. All other
parts, including Makefile, will use that version number.

src/revpi_middleware/__init__.py

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