Documentation and Tests

[klassiker]

We need more documentation regarding the configuration options and more tests for all the features we already have.

Documentation strategy:

• generate openapi using rest_framework and spectacular
• generate client using openapi-fetch

This will and should not be all of the documentation.

Testing strategy:

• generate database fixture using tooling
• generate frontend fixtures using backend tests
• perform E2E tests using Cypress

Although first steps have been made, the tests have to be extended.