Annotation to describe supported aggregation methods

A service may support only a subset of all standard and custom aggregation methods advertised in annotation ApplySupported/CustomAggregationMethods for certain aggregatable properties. If deviations from the full set could be annotated at property level, clients would be able to recognize them and avoid requests that will be rejected by the server. In particular, this would also support the special case of an aggregatable property that does not support any aggregation method, but there is a CustomAggregate annotation with the name of the property as qualifier. Then, the property could still be used in the aggregate transformation without "with", and could also be annotated with further terms.