Allow prometheus to retrieve the counter values
- Add a method to get the list of counters on the backend
- Add an endpoint on the rpc to expose the counters values in the prometheus format
- The way redis was instantiated by the fixture needed to be changed to always start a new test with an empty redis
Related to swh/infra/sysadm-environment#3164 (closed)
Migrated from D5321 (view on Phabricator)