search: introduce basic limiter
Created by: stefanhengl
This adds a limiter to our GraphQL API that limits requests from anonymous callers. The rate limit is configurable through the site configuration.
There was already a much more sophisticated, but disabled, rate limiter in place that currently undergoes testing. This new limiter is a heavily simplified version of the existing limiter which we can use for the time being.
To abstract from the implementation, I created 2 new interfaces "Limiter" and "LimitWatcher".