move sql files in the python package and update tests according to D538
Also depends on swh-storage's swh-storage!99 (closed).
This refactoring also requires a small change in vault's swh-schema.sql: create the dbversion table only if needed, otherwise this sql cannot be executed without error on the top of storages' db schema.
Related to swh-storage#1265 (closed).
Test Plan
tests should pass provided that swh-core!16 (closed) and swh-storage!99 (closed) are applied.
Migrated from D542 (view on Phabricator)