Automatically tag and upload if the changelog does not say UNRELEASED

Currently the pipeline builds and uploads sources to the :snapshots OBS project, and then the tagging and upload to the actual OBS project needs to be triggered manually by the developer.

Now that things seem to work quite reliably we can let the pipeline do the tag and final upload step on its own unless the top entry in the debian/changelog file has UNRELEASED as the target distribution.