Draft: Resolve "Add Interoperability test cases"

As written in Task 4 in the ToRT046 ISG CIM document, we want to implement the current interoperability tests in the robot framework. We also want to define a clear methodology to implement the NGSI-LD protocol itself.

We want to support a new interoperability event that gathers together the existing implementations, helping strengthening the NGSI-LD specification.