docs: generate OpenAPI specification

[daniel-mader]

Description of change

Generating a OpenAPI specification file openapi.yaml is faster, more convenient and less error-prone than having to edit it by hand for each change to the API. The file is generated by executing an automated unit test.

Links to any relevant issues

n/a

How the change has been tested

Generated openapi.yaml file provides a good DX when loaded into Swagger UI and Scalar.

Definition of Done checklist

Add an x to the boxes that are relevant to your changes.

• I have followed the contribution guidelines for this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• I have successfully tested this change in a docker environment