Ensure the existence of Grafana dashboard for worker

Created by: sashaostrikov

Either:

• confirm the existence of the Grafana panel for the new job (See Codeintel: Dependency index jobs panel in https://sourcegraph.com/-/debug/grafana/d/worker/worker?orgId=1)
• create the Dashboard if it doesn't exist

Ensure the dashboard / panel contains at least:

• the number of tasks in each status over time