journal_data: Make origin-visit optional fields to None
This sets the fields status, metadata and snapshot from the origin-visit entries to None (as per the recent model change swh-model!276 (closed))
This pulls the creation of origin-visit-status with almost the same origin-visit entries as before. the origin-visit-status dates are slightly larger than the origin-visit ones so we are able to reflect the reality of operations (first creation of origin visits, then creation of origin-visit-status associated to that origin-visit).
Related to swh-storage!938 (closed)
Related to T2310
Test Plan
tox
Migrated from D3344 (view on Phabricator)