Develop a monitoring solution for backend load

Description

The backend should have some kind of load detection mechanism, that should cause a monitoring notice to be send to the maintainers, if the load extends a certain level.

This could be done, by checking the response time of the backend itself and the search times which are sent by elasticsearch.

Explanation

Even with low user counts there can be a bug that slows down response times of the backend. We had it multiple times in the past.

cc: @krlwlfrt