Make pydantic data models more modular

[matthiasschaub]

Description

Pydantic data-models: Make models more modular. Use Union for those models when definining FastAPI request parameters.

FastAPIs swagger interface: Add multiple examples and improve documentation/description of those examples and endpoints in gerneral.

Checklist

• I have updated my branch to main (e.g. through git rebase main)
• My code follows the style guide and was checked with pre-commit before committing
• I have commented my code
• I have added sufficient unit and integration tests
  • Test for all invalid parameter combination
• I have updated the CHANGELOG.md

[matthiasschaub]

[matthiasschaub]

One further improvement would be: Drop down menu with possible parameter values for POST request examples (like the GET request examples).
Here is an issue for this: #238
I would like to tackle this in a separate PR and at another time.

[joker234]

maybe we need tests for that test 😜

[matthiasschaub]

Would probably be good :D