API first Spring Boot Service (WIP)

This Spring Boot Service will be created by the API first approach and tested with Karate. Due to missing capability of OpenAPI Generator in Version 5.0.0 the direct download of the API spec is not possible at the moment. So we will rely on using Gradle Download Task. There is also already a bug report written by joschi. And there is an open feature request for OpenAPI Generator to support OpenAPI Spec 3.1. During the writing process OpenAPI Generator was removed and replaced OpenAPI Processor.