Interaction between harvesting system and toolbox / toolbox endpoints

We need to decide how the harvesting system and the toolbox interact when crossref/datacite metadata conversion ist done in the toolbox, but the harvesting system needs the converted metadata for Archiveatica ingest. See discussion in issue #11 .

@FreundJ and I have drawn an outline how that interaction could take place over multiple steps. See https://drive.google.com/file/d/1HbVHOaY6gyz64sHo0ppMbQQHoNFBzoHg/view?usp=sharing

@dariok @tittel @sajjadhossain: Is that a feasible approach? Please comment or outline alternatives.