This PR simplifies the `test/upgrade` tool the QA team uses to test DB
upgrades.
- Removes "online migration" approach because we currently don't support
it (so it removes nginx as dependency).
- Adds a workflow to manually run this on Github actions (in case dev/QA
folks have issues with Docker on macOS, which is a common thing...)
- Adds logging to the output to ease troubleshoot (previous versions was
too quiet making it impossible to troubleshoot).