MRI release jobs

Current infrastructure provided for releasing is quite annoying to use and leaves a lot to the release manager.

Notably:

• post-release version bumps are not automatic
• the release tag does no appear in branch history
• we have no automated hooks from stage jobs to CSIT
• the amount of copy&paste/tweaks for release-merge is just pure pain
• we really want to do the whole 'mvn release:*' dance

Design and implement a pipeline which supports this.