Store active build status as assets and use it to sync jobs

[lazka]

As partly suggested by @MehdiChinoune we could try to sync the build jobs somewhat to avoid duplicated builds:

• Have a new dummy release similar to the "failed" status
• When a build starts upload a json file containing:
  • the job id, so we can check if the build is still active
  • a html log url, so we can show this on packages.msys2.org

This would allow us to build every build type on every job and scale better.

edit: (I wonder if there is a maximum length for release asset labels.. it could be used to store some json)