web-api content type is text. Should be json.

[CThuleHansen]

Ensure proper content-types.
This makes it possible to link swagger docs to the actual java object representing the json.
i.e. with just text, the automated swagger docs cannot say anything about the data:

But with json, swagger can:

I think it is possible to have multiple content-types, as it works for simulate (https://github.com/INTO-CPS-Association/maestro/blob/development/maestro-webapi/src/main/java/org/intocps/maestro/webapi/maestro2/Maestro2SimulationController.java#L217)

But it requires some plumbing (https://github.com/INTO-CPS-Association/maestro/blob/development/maestro-webapi/src/main/java/org/intocps/maestro/webapi/SimulateRequestBodyConverter.java)