Retrieve Picked Points - WebRTC

### 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](https://www.open3d.org/docs/latest/getting_started.html#development-version-pip).
- [x] I have checked the [release documentation](https://www.open3d.org/docs/release/) and the [latest documentation](https://www.open3d.org/docs/latest/) (for `main` branch).

### My Question

Is there a way to implement the functionality of **picking points** on a point cloud and retrieving the array of selected points using **WebRTC**? Or is there another workaround?

```
def pick_points(pcd):
"""Allows the user to pick points interactively in the Open3D viewer."""

o3d.visualization.webrtc_server.enable_webrtc()

print("Please pick points to define a region. Press 'Q' to finish.")

vis = o3d.visualization.VisualizerWithEditing()
vis.create_window()
vis.add_geometry(pcd)
vis.run()
picked_indices = vis.get_picked_points()
vis.destroy_window()

return np.asarray(pcd.points)[picked_indices]
```