Work attribution --- Editors and translators

[lb803]

At present, we only reference chapter author(s) in PDF metadata for work attribution:

chapter-splitter/src/modules/metadata.py

Line 38 in 8a84205

.select('DOI', 'license', 'author',

This is correct, but some of our works have also editors and translators. It would be interesting to check whether it's possible to reference these people too, steps are:

1. Check whether a metadata field exists for work editors and translator;
2. Check whether this field can be written with exiftool;
3. Dev work: query xref for data and write data to PDFs.