monitoring GeoHealthCheck itself

So who monitors the monitor?

In production environments a generic HTTP (Keyword) monitor or even another GHC instance may be used to monitor the uptime and availability of a running GHC (Webapp).

## Problem
In some cases where GHC runs with a separate `GHC Runner` instance (that continuously runs the healthchecks via APScheduler), that process may somehow die (or maybe even running but stuck somewhere). The `GHC Webapp` could still be up. There is currently no way to find out whether `GHC Runner` is actually running other than detailed process inspection (ps, docker ps, Prometheus etc).
But we would like a simple HTTP-based status check via the GHC Webapp for the Runner, that it is active.

## Possible Solution
Provide a GHC API `status` service that reports recent activity of GHC Runner. For example the number of runs in the last N minutes. This is easily realized with a query. (Easier than inspecting external processes/Docker containers). GHC or any HTTP-uptime checker could check for a keyword like `runs: 0` meaning no runs in last N minutes. This indicates that GHC Runner is not running (or maybe even running but stuck somewhere).