Documentation REST API

[SelinaBuff]

We want to document our REST API for the scrumlr backend.
For that we want to create a OpenAPI file. Here we have two options

1. Let the OpenAPI file be generated with e.g. https://github.com/swaggo/swag. For this approach we need to annotate all API endpoints.
2. Write a OpenAPI file and let the REST API be generated and implement the generated interfaces with e.g. https://github.com/oapi-codegen/oapi-codegen. This would require to reimplement the API.

This file could then be used to host a swagger page in development mode.

• Choose a tool
• Setup an OpenAPI file
• (Would be nice) Setup a Swagger page for development mode