storage/writer: refactor JournalWriter.content_add to send model objects
to the journal writer, as it already does with other objet types (instead of dicts).
Migrated from D2803 (view on Phabricator)
Staging instance, all changes can be removed at any time
to the journal writer, as it already does with other objet types (instead of dicts).
Migrated from D2803 (view on Phabricator)