Allow ponos agent to use RetrieveWorkerRun

Refs https://redmine.teklia.com/issues/4832

As we are building a ponos agent for JeanZay, we need to start fully offline workers, so the worker itself is not capable of retrieving its own configuration. The ponos agent needs to retrieve the configuration for the worker, and provide it locally (through a JSON file).

To do that, we need the RetrieveWorkerRun endpoint to be accessible by ponos agents.