Allow unspecified parameter types in non-implemented microservice operations

[frademacher]

Currenty, we prevent the usage of the built-in unspecified primitive type in microservice operation parameters. However, for non-implemented microservice operations it may make sense to allow parameter typing with the unspecified type. For instance, this approach would foster the agile specification of microservice APIs.

Syntax example:

functional microservice org.example.Service {
    interface ExampleIface {
        noimpl notFinishedOperation(sync parameterTypeToDecide: unspecified);
    }
}