Actions storage:
- Open cache_content_get to retrieve contents in cache
- sql/upgrades/080: Add stored procedure to read contents from cache

Actions archiver:
- d/control: Add dependency to archiver on python3-swh.objstorage.cloud
- Renamed Archiver(Director|Worker) to
ArchiverWithRetentionPolicy(Director|Worker)
- Add ArchiverToBackend(Director|Worker)
- Add new celery task dedicated for new workers
- Update docstring details

Related T555