Doc datamodels

[jkeupp]

Hey there,

This is the datamodels doc page i'd like to propose. You may recall from two weeks ago, that there was an issue with the datamodel in fastapi that yielded 422 always. This was actually due to running fastapi via main in the script itself... running it via uvicorn [file]:app resolved the issue.

I've not yet changed anything in mkdocs, as I think we should do this once all the components are there.