add xml reference as button on document page

[marcblanchet]

Description

I always struggle to get the proper <reference> for a draft that I'm referencing in my own draft. I know it is available like in bib.ietf.org (and maybe other places), but I always go to the datatracker for that draft (to know its status, get the right version, ...). It would be very valuable and probably not that lot of work (given already implemented the bibtex button) to have in datatracker/doc/draft-... a new button in the "Formats" line to provide such bibxml info of that draft.

Code of Conduct

• I agree to follow the IETF's Code of Conduct

[pselkirk]

I just issued a PR for a button. In the meantime, the bibxml is already there (just without a UI), and you can enter the URLs directly, e.g.
https://datatracker.ietf.org/doc/bibxml3/draft-blanchet-dtn-email-over-bp.xml
https://datatracker.ietf.org/doc/bibxml3/draft-blanchet-dtn-email-over-bp-02.xml