add json schema to model docu and swagger api docu

[JJ-Author]

from @manonthegithub : For json-ld it would be good to have jsonschema docs. then people can generate their own client very easily. Most of languages have json schema libs which allow to generate code and models based on the schema
https://json-schema.org/learn/getting-started-step-by-step#create.

[JJ-Author]

cool idea: that could be another tab additionally to shacl, owl, example.
but also fix the weird output that is shown under "schema" in swagger UI https://dev.databus.dbpedia.org/api/#/Artifact/create-artifact
i saw tools that derived the json schema from an example. so maybe this can be automated. I dont know how good it works for jsonld, but maybe there are also tools who can do it based on owl/shacl for jsonld.