convert-merge-rails: file issue at branching point
When the upstream merge process reaches an upstream minor version branching point, we have work to do: typically starting a Heptapod release branch.
Even in the current catch-up phase during which not all upstream minor versions give rise to a Heptapod release, we still have to bump Omnibus and create a tag in order to be able to come back to it and release a posteriori if needed for data migrations.
In all cases, it is better to stop the upstream merge process, and filing an issue with the "Upstream merge" label does exactly that. Since we have a template for the release branch creation, it would spare us a manual action to use it right away.