Add required calibration/configuration artifacts to container

Now that the FileLoader in athena is able to use cached calibration files, I think the next steps are:

• issue one dd4hep call in each detector path explicitly during container build to prepopulate that with cached files !253 (merged),
• allow for FileLoader to parse environment variables as part of the cache path EIC/detectors/athena!319 (merged),
• allow for FileLoader to use a fs::recursive_directory_iterator to find the cached file EIC/detectors/athena!320 (merged).

This would then add to e.g. /opt/detector/athena-deathvalley/share/athena/calibrations/

• an actual file 8b21c068916be3c4,
• a link materials-map.cbor to 8b21c068916be3c4.

A FileLoader call in any other directory would find the actual file above by using cache:$DETECTOR_PATH, with DETECTOR_PATH set to /opt/detector/athena-deathvalley/share/athena (as already the case now) and link to it in the $PWD/calibrations. Existing json files distributed through the repository are still found as before.

I don't think there is a way inside FileLoader to get access to the top-level athena.xml path.