[python] Generate `pyproject.toml` for our packaging, slowly deprecate `setup.py`

[iscai-msft]

The python world is moving from setup.py -> pyproject.toml, so we should go with the tide. For our new package generations, I think we can switch entirely over to pyproject.toml instead of setup.py. This will gradually shift the makeup of our packages to pyproject.toml. Please make note to publicize this at least in the Python team's chat