Modernize cookiecutter

[Zeitsperre]

Overview

Changes:

• Replaced setup.py with pyproject.toml with differing backends for the top-level and templates (setuptools and flit)
• Removed many obsolete configuration files
• Updated GitHub Actions versions to their latest commits
• Dropped support for Python older than version 3.9
• Added pre-commit configuration to the template
• Updated the licensing to add a preamble to the __init__.py
• Replaced bump2version with bump-my-version
• Modernizes Python code to be Python3.9+ compliant

Related Issue / Discussion

https://peps.python.org/pep-0517/ https://flit.pypa.io/en/stable/ https://pre-commit.com/