Testing Façade API metadata schema

[jonathan-r-thorpe]

The current schema for the Testing Façade API question-schema.json has a metadata property currently used by the IS-04 and IS-05 Controller tests for the purpose of fully automated testing. As the number of Controller test suites expands, and the type of metadata required for automated testing becomes richer, the schema for this metadata property may need to be refactored, possibly into a set of 'mix in' schemas that test suites could opt into (similar to the transport_params schema in IS-05).