Add support for kafka journalization of the ProvenanceStorageInterface

the new ProvenanceStorageJournal is a proxy ProvenanceStorageInterface that will push added objects in a swh-journal (typ. a kafka).

Journal messages are simple dicts with 2 keys: id (the sharding key) and value (a serialiazable version of the argument of the xxx_add() method).

Depends on !152 (closed) Related to #4616 (closed)

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Migrated from D8657 (view on Phabricator)