Switch from setup.cfg to pyproject.toml

[wilbrdt]

Feature Request

Since PEP 621 has been adopted by the python community, pyproject.toml configuration file is now the go-to config.

We may need to install flake8-pyproject to be able to configure flake8 through pyproject.toml if not using Ruff already (issue #480).

See this PR on Joanie for inspiration