[Test Suite] Investigate usage of Castle Mock
CastleMock is a service that allows to easily mock REST APIs and SOAP APIs.
As we want to have test suites with as little dependencies as possible, but also mock as little as possible, this is a good trade-off.
We will need to configure it on a local machine and then use the config directory to bake it into a Docker image, so we can run it locally and also include it in the CI pipeline.