The `graph.Json` should be modeled as `Edm.Untyped`

[andrueastman]

The graph.Json type is used to model untyped Json data that could be of any typed.

This leads it to being converted to an object type microsoft.graph.json which is not accurate at representi possible primitive and collection types when converted to the openApi description.

Once the conversion library(Hidi) supports handling of Edm.Untyped in csdl metadata, we should add a transform to replace the properties/parameters types from graph.Json to Edm.Untyped for openApi based scenarios.

This will enable the converter to correctly represent dynamic types in the open api metadata.