Partially related with https://github.com/jupyterhub/repo2docker/issues/1427 The project uses [`setup.cfg`](https://github.com/jupyterhub/repo2docker/blob/5870d2bc35a5c48ce886f50396dead7f5f31b3c9/setup.cfg) and [`setup.py`](https://github.com/jupyterhub/repo2docker/blob/main/setup.py) for installation. [`pyproject.toml`](https://packaging.python.org/en/latest/specifications/pyproject-toml/) was defined almost 10 years ago in [PEP 518](https://peps.python.org/pep-0518/). Should we adopt `pyproject.toml`?
