/readiness endpoint

[nhoening]

This endpoint can be used to monitor if the container could perform its jobs.

From a Kubernetes-bases article:

Readiness probe. This is for detecting whether the application is ready to handle requests. If a readiness probe fails, Kubernetes will leave the pod running, but won't send any requests to the pod.

I'm considering whether this would be a good (central) place for monitoring if all tasks have been run in a sufficient manner. If not, we can also add a different endpoint for that, e.g. /completeness

[nhoening]

We got /api/v3_0/health/ready, from #416 so I am closing this.