Add headers to ModelGraphics

My API with gltf models uses tokens and absence of headers make a real problem for my case. I have checked that ModelGraphics uses the Model.FromGltf method, which contains this property. So i sure that adding 1 property does not demand a lot of efforts, but it will help me (and others). And i know that i can use Primitive API, but i`m using features from Entity API. Or does someone know how to cast Model to ModelGraphics?

Start by tracing ModelGraphics and its use of Model.FromGltf, then compare the existing headers property exposed through the Primitive API. Done means Entity API users can provide headers for glTF model requests through ModelGraphics; the issue names no file or test, so locate the relevant implementation and coverage first.

Written by the indexing model from the issue text.