bug#45300: [Suggestion] Add option --with-patch

[Philippe SWARTVAGHER]

Hello,

We already have `--with-branch=`, `with-commit=`, ... An additional
option could be `--with-patch=package=add-extra-feature.patch` which
would apply the patch file `add-extra-feature.patch` located in the my
current directory to the sources of `package` before Guix starts
building `package`.

This would bring the possibility to easily share patches (for tests,
reviews, ... for instance) without having to commit the patch in the
source repository of the package, without changing the package
definition, and without applying ourselves the patch to our local source
repository of the package.

Thanks !

-- 
Philippe SWARTVAGHER

PhD Student
TADaaM team, Inria Bordeaux Sud-Ouest