Add panel with job burndown rate to Job dashboard

[physikerwelt]

In Grafana, we see the total number of jobs and the number of jobs added, but not the number of jobs completed. Effectively, we need the derivative of the Total consumer group lag.

[timconrad]

Can be changed here:
https://github.com/MaRDI4NFDI/portal-k8s
-> infrastructure/grafana-dashboards/kafka-mardi-dashboard.yaml