Add ability to enable verbose mode for VCS tools

[jackwhelpton]

What's the problem this feature will solve?

I am currently struggling to debug an issue with pulling dependencies from GitHub Enterprise, probably owing to auth errors. However, the details are hidden because pip is executing git with the -q flag, even when pip itself is running with -vvv.

ERROR: Command errored out with exit status 128: git clone -q 'ssh://****@github.***com/***/***.git' /tmp/pip-install-8sx2d1op/*** Check the logs for full command output.

This is the inverse problem to #8460.

Describe the solution you'd like

pip install -> git clone -q
pip install -v -> git clone
pip install -vv -> git clone -v

The same change could be made for the other git commands, although git clone is the most critical as it is where auth errors will first show up.

Alternative Solutions

Not really. I've looked into the code to validate the current behavior, and am game to help make this change, although I need to ascertain how to plumb the verbosity level into the VCS class. In the meantime I may hack the pip source on the remote machine just to show up the Git errror.

Additional context

[uranusjr]

Sounds good to me, except I may choose to put git clone -v under pip -vvv instead (just personal preference).

[pradyunsg]

Likewise.