Add Grafana dashboard for loose foreign keys processing
Per gitlab-org/gitlab#346481 (closed)
This has been a protected playground dashboard at https://dashboards.gitlab.net/d/RKrvPFp7k/loose-foreign-keys?orgId=1 for some time and we would like to have a permanent dashboard for this data so we can get a sense of how the overall loose foreign key processing is going as we scale.
I chose to keep it simple and just use the timeseries defaults which is slightly different from the original dashboard which used stacked bar charts. I don't have a strong preference but I think unstacked lines work fine.
I also kept it under sidekiq/ as all of this work happens in a sidekiq job so seemed to be part of the sidekiq service.
Previous playground dashboard
https://dashboards.gitlab.net/d/RKrvPFp7k/loose-foreign-keys?orgId=1
New permanent dashboard
Temporary preview URL https://dashboards.gitlab.net/dashboard/snapshot/JPsMMuN4OzXbnG85zRM16xBkgMuBESmB?orgId=1
