Swagger UI inconsistent to current behavior for submodel controllers

[tom-rm-meyer-ISST]

Description

Current behaviour

During #514 we realized that the swagger ui often shows incorrect response bodies (e.g. return entity instead of empty).

All submodel api controllers are subject to this:

• production-request-api-controller
• demand-request-api-controller
• item-stock-request-api-controller
  It may also make sense to add desccriptions to these controllers, that these are meant to be called by partners through the EDC.

Expected behavior

Swagger UI should be in line with the implementation

Steps to reproduce the Bug

• build backend
• run local deployment
• open swagger-ui of customer
• compare controller with backend implementation