Use a declarative approach for setup.py/setup.cfg

[tomschr]

Situation

The setup.py file shows its age. After several years, the Python ecosystem provides a more declarative approach. This is the more recommended way and is not yet covered in setup.py and setup.cfg.

Suggestion

• Use the declarative config as shown in the setuptools documentation.
• Move specific pytest configuration into pytest.ini
• Move specific bumpversion configuration into .bumpversion.cfg