Add OpenAPI support to document endpoints

Problem/Motivation

To improve the documentation of the API endpoints provided by the module, a yml-file should be added to describe endpoints according to the OpenAPI standard.

Steps to reproduce

• Check the code repository for an OpenAPI-complicant documentation yml file

Proposed resolution

Add an OpenAPI-compliant yml file

Remaining tasks

• Add an OpenAPI-compliant yml file

User interface changes

• None

API changes

• No changes, but documentation added.

Data model changes

• None