Add more declarative config

[blink1073]

Ideally we shouldn't need a setup.py file.

• We can use from importlib_metadata import version; version('<name>') anywhere where we're using python setup.py --version, and we can get the name from setup.cfg or pyproject.toml if available, and fall back on python setup.py --name.
• We can add data_files config using our better tuple and glob handling
• We should also handle ensured_targets
• Ideally we could replace all of jupyterlab/setup.py