Add range constraint and reference for clouds

Currently the range of the clouds (oin oktas) is only limited by the annotation. We could introduce an actual constraint for this struct to have a better automatic range checking.

Also there is not refernce given for the oktas. There is already one in OSI, which can be used: https://github.com/OpenSimulationInterface/open-simulation-interface/blob/master/osi_environment.proto