fix(*): jats exports doi instead of id if we have one

While we correctly get the DOI out of the article metadata, we weren't exporting it as the article ID in JATS – instead we were defaulting to id, which could also be validly set as the article-id type ( https://jats.nlm.nih.gov/archiving/tag-library/1.1d1/n-7s30.html ). This change uses the DOI as the article ID if we have one; if not, it tries to fall back to the id.