Modernize setup.py to pyproject.toml

[rngadam]

This warning is shown when launching:

 /usr/local/bin/tails-server:4: DeprecationWarning: pkg_resources is deprecated as an API. See https://setuptools.pypa.io/en/latest/pkg_resources.html

Assuming that this is because setup.py is used as a build frontend in addition to build backend and needs to be modernized:

• https://packaging.python.org/en/latest/guides/modernize-setup-py-project/
• https://packaging.python.org/en/latest/discussions/setup-py-deprecated/