Investigate the openapi-generator

[Tschonti]

https://openapi-generator.tech/
After #48 is merged, investigate how we can use the openapi.yaml file to generate code with openapi-generator in this and in future projects, including:

• generating client-side functions to call the endpoints with axios (used by React/next)
• generating abstract classes/interfaces for serverside boilerplate code (used by nest.js)
• generating Postman collection