This allows to scrub multiple db instances.
For production environment, this means:
- primary db (belvedere)
- secondary db (somerset)
For staging, that stays as before, the service will still get renamed though, e.g
swh-scrubber-checker-postgres@directory-0 becomes
swhscrubber-checker-postgres@primary-directory-0.
I'll attend to the clean up of old services manually.