Add model and data config files

Created by: asogaard

By setting up a standardised syntax for model and data config files (e.g. using pydantic), building off what little is currently in https://github.com/icecube/graphnet/tree/main/datasets makes it easier to reproduce results, make their provenance transparent, and share configurations between users.

• Data/DataConverter config
• Dataset config (#353)
• Model config (#309)