Draft: [Webservice] Prepare for new calibration_configurations structure

I'm planning a reorganisation of the file structure in the calibration_configurations repo, to organise config by instrument rather than by cycle. This prepares the webservice code to use the new structure, while still working with the current structure as well, so we don't have to change both simultaneously.

And this is what the config change would look like: https://git.xfel.eu/detectors/calibration_configurations/-/merge_requests/37