Add trivial command line for the PyPI loader
Very helpful for debugging
Depends on D411
Test Plan
python3 -m swh.loader.pypi devpi-common does something useful
Migrated from D412 (view on Phabricator)
Very helpful for debugging
Depends on D411
python3 -m swh.loader.pypi devpi-common does something useful
Migrated from D412 (view on Phabricator)