We should add mentorship-related metrics to the [Growth team product KPIs dashboard](https://grafana.wikimedia.org/d/bSDW0wJ7z/growth-team-product-kpis?orgId=1&var-tasktype=All&var-wiki=cswiki&var-questiontype=All&var-variant=All). Metrics to include:
* Number of automatically assigned mentors
* Number of monthly registered newcomers divided by number of automatically assigned mentors
* Number of inactive (automatically assigned) mentors, where an inactive mentor is defined as "did not save any edit in the last 30 days"
==== Acceptance criteria
[ ] [Growth team product KPIs dashboard](https://grafana.wikimedia.org/d/bSDW0wJ7z/growth-team-product-kpis?orgId=1&var-tasktype=All&var-wiki=cswiki&var-questiontype=All&var-variant=All) includes the metrics defined in the task description