Stub test connectors

[rhuss]

Mock test connectors are simple connectors which can be used at both ends of an Atlas-mapping to easily try out and test uses case.

These connectors should be easily usable during design and runtime

[zregvart]

I would perhaps call them stub connectors, I think this is something we could model like wiremock is modelled, that is have a REST API that controls how the connector behaves, I think this will help when used in E2E tests.