Include DOI field from Zotero

[wlpotter]

The DOI field from Zotero is not being added to the TEI.

TEI recommends a type of “DOI” for such cases, and just the ID portion of the DOI: https://www.tei-c.org/release/doc/tei-p5-doc/en/html/ref-idno.html (and examples)

Example:
https://syriaca.org/cbss/FNQTRRKH.xml
https://github.com/srophe/syriaca-data/blob/master/data/bibl/json/FNQTRRKH.json (l. 78)

Possibly we'd also want to add a ref element with @target with the URL for the DOI lookup? Or is this something we supply in the Gaddel transform?

[wlpotter]

We want to add the DOI when it's from the doi field in Zotero, or the DOI key from the extra field (we use the latter for books and book sections since Zotero does not supply a dedicated DOI field for those item types)