bug#38320: Cuirass: Allow to use authenticated Git repositories as inputs

[Clément Lassieur]

Hi,

I'd like to use private Git repositories as inputs, authenticated with
SSH.

I think it is important because it would encourage users to use Cuirass
for other purposes than just a CI tool to build Guix packages.  I'd like
to see it as an alternative to Jenkins, it would make its user base
broader.

My use of Cuirass, for example, is to do continuous integration on my
own personal projects.  So each of my inputs is a personnal private
repository, and each time one of those inputs has a new commit, the
'proc' will give Cuirass a derivation of the Guix package corresponding
to the updated input, with a modified 'origin' so that it matches the
new input.

My workaround for authentication is to use local repositories, updated
with an external cron task.

I think there are small modifications to do to (guix git) and (git
clone).

Cheers,
Clément