How to sync up the cameras of multiple sceneWidgets in gui?

### Checklist

- [X] I have searched for [similar issues](https://github.com/isl-org/Open3D/issues).
- [X] For Python issues, I have tested with the [latest development wheel](http://www.open3d.org/docs/latest/getting_started.html#development-version-pip).
- [X] I have checked the [release documentation](http://www.open3d.org/docs/release/) and the [latest documentation](http://www.open3d.org/docs/latest/) (for `master` branch).

### My Question

I'm currently trying to sync up the camera of multiple viewport inside a single window, meaning if i rotate the camera on one viewport the cameras of all other viewport move synchronized with it. I used the implementation from this [issue](https://github.com/isl-org/Open3D/issues/999#issuecomment-1405048921). I've multiple things looking at the documentation but can't create a working solution.