Plan, out of [1] diff:
- [ ] scheduler-node (scheduler0.staging): stop the old journal client
- [ ] Wait for all tasks to finish
- [ ] Stop and remove celery workers and queues
- [ ] D7928: Rework puppet manifest to update the new way of running the indexer
- [ ] scheduler-nodes: Clean up old service
- [ ] workers: Deploy new journal client service on workers
- [ ] workers: Start the new journal client services [2]
[1] D7899
[2] It can reuse either the group_id to avoid re-indexing, or use a new one to reindex
everything (to solve old previous temporary failures we ever had)