Add .flake8 and remove requirements & setup files
This commit deletes the requirements_tests.txt, requirements.txt, setup.cfg and setup.py files as they are not used anymore. We only use pyproject.toml now. It also adds the .flake8 configurations as a replacement.
Related to https://github.com/chaoss/grimoirelab/issues/532
Coverage increased (+0.08%) to 97.871% when pulling c02f56053c787febe9a6819f33ea8f99754fdc18 on vchrombie:532-remove-files into 950ff4f2ef5a24be22bb4fa3a3f597c5352362ff on chaoss:master.
I will update the README.md file too to match it with the other PRs.
@jjmerchante do you mind reviewing this PR when you have time? I aligned it with the other PRs for the grimoirelab tools.