feat: Add SceneKit

### Feature:
- now that SwiftUI 2.0 has `SceneView` supported by SceneKit, we can add a row under `Maps` for an example of SceneKit.

### Implementation
- All we need is a model with extension `.usdz` and a few lines of code to implement this feature.
you can preview implementation in the readMe of [this repository](https://github.com/aaryankotharii/iPlanet)

Start by reviewing the existing Maps examples and the implementation shown in the linked iPlanet README. Add a SceneKit example using a .usdz model and place its row under Maps; it is done when the example appears there and can be previewed in the app.

Written by the indexing model from the issue text.