Query generation: add descriptions to enable function calling-like behaviour

[slobentanzer]

The default process does not consider annotations on the entities in the schema information. To allow behaviours more informed by the context of the entities in the graph, the schema config could also allow description fields for nodes, edges, maybe even properties, to enable deeper explanation of the meaning of each field to the LLM at query time, potentially improving contextual understanding in query generation, in the same way as the Pydantic class in function calling operates.