This is an extension of
https://github.com/python-poetry/poetry/pull/6724. I think `pip install`
invoked by poetry should never ask for user input.

Motivation is that it happened to myself and a number of colleagues many
times that poetry got seemingly stuck while it was just waiting for a
user input because of a private pypi repository that needed
authentication.

I hope this is a valuable contribution to a tool I like a lot and would
like to use more and more :)