Add a Hydra primitive type for Arnold cameras and create UsdImaging adapters for camera schemas

**Describe the feature you'd like**
We should add a custom hydra type for Arnold camera schemas and create adapters for our custom camera schemas. We also need to make sure that in other render delegates (mainly HdStorm) there is still an approximate preview of the camera, like using a perspective camera with a matching transform and parameters that are shared between camera types.