Automatically add setuptools to buildInputs for legacy projects

[Atry]

Describe the issue

According to PEP-517:

https://peps.python.org/pep-0517/#:~:text=affected%20by%20this.-,If%20the%20pyproject.toml%20file%20is%20absent%2C%20or%20the%20build%2Dbackend%20key%20is%20missing%2C%20the%20source%20tree%20is%20not%20using%20this%20specification%2C%20and%20tools%20should%20revert%20to%20the%20legacy%20behaviour%20of%20running%20setup.py%20(either%20directly%2C%20or%20by%20implicitly%20invoking%20the%20setuptools.build_meta%3A__legacy__%20backend).,-Where%20the%20build

If the pyproject.toml file is absent, or the build-backend
key is missing, the source tree is not using this specification, and
tools should revert to the legacy behaviour of running setup.py (either
directly, or by implicitly invoking the setuptools.build_meta:__legacy__
backend).

However, currently poetry2nix does not add setuptools to buildInputs for projects without a pyproject.toml, as a result, the dependencies to setuptools have to be configured in https://github.com/nix-community/poetry2nix/blob/master/overrides/build-systems.json

It would be nice to automatically add setuptools to buildInputs for projects without a pyproject.toml in terms of PEP-517 compliance.