Use `pyproject.toml` for configuration?

In https://github.com/dask/distributed/pull/5720 @ian-r-rose and @gjoseph92 brought up switching some (maybe all?) of our various tool configuration (e.g. `pytest`) from `setup.cfg` to a `pyproject.toml` file. Some projects, e.g. `pytest`, explicitly recommend against using a `setup.cfg` file in favor of other configuration files like `pyproject.toml` https://docs.pytest.org/en/6.2.x/customize.html#setup-cfg. I'm not familiar with `pyproject.toml` so can't speak to various pros and cons -- opening up an issue to see if there's interest in using `pyproject.toml`