XML-Export for DOI registration of Attachments

[AndyDaniel1]

Idea for a smaller solution: Implement a xml export for a da|ra / datacite valid xml in the attachment section. This could then be imported into da|ra without additional manual effort.

All necessary metadata is already collected in the MDM input mask, at least for DMR (the doi has to be predefined in the input mask). Only the type and the landing page (text: Data and Method Report) has to be filled in the XML by the MDM.

XML-import-mask (here da|ra example):

Maybe we could implement checks if the doi put in the inputmask is already registered (should be easy).

It makes sense to wait until #3240 is resolved but the general idea should be working for DataCite as well. In Data Cite the doi proposal and the landing page has to be filled in manually in the case of the xml-import, but this shouldn't be a deal breaker.

--> Has first been part of #3137 (#3137 (comment))