Better handling of installing older Frappe apps due to pip deprecated behaviour

[gavindsouza]

I came across the following warning while setting up requirements for a bench

DEPRECATION: Legacy editable install of erpnext_germany==15.13.0 from file:///home/gavin/Desktop/v2/benches/v15-dev-bench/apps/erpnext_germany (setup.py develop) is deprecated. pip 25.1 will enforce this behaviour change. A possible replacement is to add a pyproject.toml or enable --use-pep517, and use setuptools >= 64. If the resulting installation is not behaving as expected, try using --config-settings editable_mode=compat. Please consult the setuptools documentation for more information. Discussion can be found at https://github.com/pypa/pip/issues/11457

While app maintainers can migrate their existing apps, those apps that aren't maintained anymore will become uninstallable.

However, bench can take care of this by passing --use-pep517 conditionally if the app requires it - maybe when setup.py exists or something