[Poc] tox usage proposals

[kuchichan]

This is just a proposal of tox integration into Ariadne. It could speed up local development especially in pre-commit phase (testing & linting) for multiple python versions.

tox  # for mypy, black, pylint & tests against all versions
tox -e lint # mypy, black & pylint for basepython
tox -e tests # run tests with coverage

This proof of concept can be extended easily to GH actions