Have an official upstream Git repository for DAVE

Originally created by @sajolida on #12582 (Redmine)

So far on https://git-tails.immerda.ch/ I only see one repo for DAVE: ma1/download-and-verify-extension.

If we end up with more people than Giorgio working seriously on this code, then it would be good to have a master repo that would be consider “upstream”, no?

And named accordingly. Maybe https://git-tails.immerda.ch/download-and-verify-extension/.

Related issues

• Related to tails/tails#8531