Add example values to swagger documentation

[nilsfs7]

While building on the rest API I noticed its documentations lacks example values. This made integration hard because I was not able to receive proper json responses for all endpoints. Especially for /duties/raw/proposing as you need to be lucky to be provided with data.

[TobiWo]

Just for my reference:
Implementation example: https://fastapi.tiangolo.com/tutorial/schema-extra-example/#extra-json-schema-data-in-pydantic-models