Add a revision_id_from_vcs() method to the Storage
This endpoint allows to query the storage for known revisions from
their original VCS type intrinsic identifier.
The underlying data structure is filled in `revision_add()`.
Related to T2849.
Missing:
- [] cassandra implementation,
- [] inmemory implementations,
- [] consistent names,
- [] more tests,
- [] migration scripts,
- [] other stuff