finish multi-stage build

[duncdrum]

a continous multi-stage build for :latest would be fully containerized.

Relying on CI for log manipulation (see #5 ) and getting the sources is a stop-gap for testing.

[duncdrum]

make :release and :latest actually meaningful again.

[duncdrum]

options:

• create another CI workflow to create a tar distribution and share this via artefacts
  • PRO: less clutter
  • CON: won't allow folks to clone this repo and run a build without having a parallel clone of exist somewhere
• Fully containerised (have a maven image, which clones exist, runs the build to create a tar)
  • PRO: fully containerised an isolated
  • CON: lots of clutter,
  • CON: make sure that builder stage can actually use maven .m2 cache on CI, so we don't have to download the internet for every build and fail because of network timeouts

In either case, we need:

• a solution that lets us checkout git tags for building :release
• a cron job for :latest and for :release
• builder needs to be multi-arch
• decide to either reuse exist-db org log modifications or roll a different one here.
• documentation for how to do this locally and what is supposed to happen.