Bugfixes for connectors

[josvandervelde]

1. Updating example connector resources, to include all fields (mainly educational resource json)
2. Bugfixes for HuggingFace, Openml and Zenodo. They all run fine now.
3. To make that possible, I changed all NamedRelations to be always lowercase. E.g. keyword. This means that keyword "AI" is changed into "ai". This fixes some weird errors --> using mysql we got an integrity error if you first add "AI" and then "ai", although "SELECT * FROM keyword WHERE name = "AI"` doesn't retrieve the keyword with name "ai".
4. Some quality of life improvements: added profiles to the docker compose (making it easy to not run the connectors), and throwing existing state of connectors away if the database is empty

In another PR I'll fix the "Permission denied" errors that you get when running the code for the first time.

[Taniya-Das]

Looks good