Migrate `setup.py` and `setup.cfg` to `pyproject.toml`

[sarahmish]

Migrate from the project configuration in setup.py to a more declarative standard in pyproject.toml

• Currently setup.py and setup.cfg are used to specify the project metadata.
• pyproject.toml is a new standard way adopted by the pythonic community of specifying project metadata, removing the need for all these files. All the project metadata should go in this file.
• pyproject.toml is compatible with other modern packaging and dependency management projects, like Python Poetry.