If you want the archiver to have cloud abilities, install the
package python3-swh.objstorage.cloud on the server as well.

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

Summary:
This API currently only concern the directories as it uses the first draft of the cooker.

Ref T532
Depends on D102

Reviewers: #reviewers!

Maniphest Tasks: T532

Differential Revision: https://forge.softwareheritage.org/D108

Summary:
This first version does create a compressed folder of an archive
directory but is not linked to any API or notification system.

This diff is submitted for architecture and code review and will evolve.

Reviewers: #reviewers!

Differential Revision: https://forge.softwareheritage.org/D102

As for python3-swh.storage.archiver, the runtime dependency on
python3-swh.core is the implicit one from python3-swh.storage.

The same note about splitting repository and adding explicit dependency
applies.

Related T557

Closes T460

Update the setup.py file in order to add the new created directory 'swh/storage/checker'

Closes T404