Re-introduce the swh.core dependency in swh.model[cli]

This allows the swh identify command to work again.

Close #2288 (closed)

Test Plan

create a fresh venv, install swh.model from checkout, swh identify works

---

Migrated from D2686 (view on Phabricator)

requirements-cli.txt

+swh.core
 Click
 dulwich