[bug#53828] [PATCH v2] import: opam: Allow importing local files.

[Julien Lepiller]

As you can see, I've reworked the patch a little. Instead of a special
#:file argument to the importer, I simply create an opam repository out
of a given "project" (if you have a better name...). A "project" is an
upstream source repository, either a local checkout or a remote git
repository, that contain .opam files.

The new version of the patch scans the project for opam packages and
adds them to a local repository. When importing recursively, they
become available, so countrary to the previous patch, you can use this
for recursive import even when multiple packages are not in the opam
repository but in the project (some projects split their code into
multiple opam packages, like coq for instance). You can specify
--scan-project multiple times, so you can import from dependent repos
too.

WDYT? :)