Make archiver have a more symmetrical behavior treating storages as potential sources & destinations at the same time

The archiver needs to be updated in order to follow the specification changes (see archiver-blueprint.md, !32 (closed))

• The archiver now treat all storages as potential sources and destinations for the archival of a content.

  • Storage with the content can be used as source and storage without it may be destination of an archival if the retention policy is not reached yet.

• Director does not take into account the ongoing status and create batches of contents that //may potentially// need an archival. Meanwhile, the Worker now do this check and treat the ongoing status as missing if the delay is elapsed, or present if not; assuming the archival will succeed and the content will be copied in the future.

  • The director is now much simpler so it can generates lighter messages that are queued more quickly; while the workers behavior was already the same.

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Migrated from T512 (view on Phabricator)