Introduce the Caldera API client

[mpboom]

In order to add the Caldera functionality we are planning, we want to introduce an automatically generated API client. This is based on the Swagger (OpenAPI) spec that is provided by Caldera. This specification contains errors; therefore we wrote a script to alter it.

This issue should spawn to PRs:

• One to add the actual generation/patch scripts
• A separate one to introduce the client itself (as this will yield many code changes)