Plan:
- Push this commit only in staging for now (when accepted)
- scheduler0.staging: Stop current journal client service
- Run puppet on scheduler0.staging to redefine the journal client service (as this here)
- Run this on staging workers to stop the old worker service (and declare the swh-journal-client service on workers)
This also adapts the instance.pp profile to clean up missing parts.
Related to T4282