Use Zenodo API to auto-register and update analysis DOIs

Aligned with OpenMAPP e-infrastructure plans, and a question I got at the UK HEP Forum last week about citeability, we should get and maintain DOIs for our analysis collection. Obviously we don't want to do that by hand, and we can't issue our own DOIs -- it requires an official registration authority and usually payment. But it is free via Zenodo and they have an HTTP API: https://developers.zenodo.org/

So, we should add a script and a release-process step that registers/updates each analysis DOI... for speed, likely only when updates occur, so it would be sensible to integrate with the analysis-diff mechanism. There doesn't seem to be a way to use Rivet's Zenodo entry as an "umbrella" category for all the analyses, but they can be registered as related to that project; maybe there's a better way?