Make use of example files for each type in registry

[ml-evs]

• Make sure the URLs are resolvable through Fly (probably pointing to GitHub raw links)
• Add the files as examples in the file types models and expose them for validation
• Validate entries in the data folder and make sure they correspond to registered file types

[PeterKraus]

This would mean that a CI in the registry repo would use the api package to check whether the files in the marda_registry/data/lfs folder can be matched to filetypes and processed using the extractors in the registry.