Add monitoring and alerting for swh-scheduler-journal-client lag

Using the existing prometheus metric scaffolding in puppet + icinga2 for the relevant consumer groups?

cc. @guillaume

changed milestone to %Provide a management-friendly monitoring dashboard of services [Roadmap - Tooling and infrastructure]

added activity::MRO label

assigned to @guillaume

mentioned in commit swh/infra/puppet/puppet-swh-site@ce217d41

mentioned in merge request swh/infra/puppet/puppet-swh-site!625 (merged)

I also added monitoring and alerting for swh.search.journal_client-v0.11 and swh.counters.journal_client.

added 2h of time spent

closed