Redefine handle_messages method in the DeduplicationJournalClient class to pass serialized and deserialized objects to the process_single_swh_object method

• This is related to the following comment
• The handle_messages method should be redefined in the DeduplicationJournalClient child class so that it allows passing both serialized and deserialized objects to the process_single_swh_object method
• This will help us to avoid the extra serialization call