add requirements file for python libs

[vincent-agi]

I had requirements.txt file to simplify project installation

[philpep]

Hi, requirements, including test requirements, are already defined in https://github.com/lowatt/lowatt-enedis/blob/main/pyproject.toml#L40

So to develop you just have to run:

pip install -e '.[test,typing]'
flake8 && mypy && pytest

Altenatively tox can be used:

pip install tox
tox