More examples for detect_planar_patches

### 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

Hello,

I am looking for more examples on different point clouds for `detect_planar_patches`. The method is absolutely unusable for me on a relatively simple pointcloud, either downsampled or not, with normal estimation from `open3d` as well. It either does not detect any plane or detects some random planes that do not seem to be related in any way with underlying surfaces.

If the method assumes that point cloud should have some specific features (point density, normal estimation quality etc), I think it is better to write it to documentation. It is also better to have more examples in order to give a feel whether the method would work or not.

I am detecting just simple rectangular box in the scene and it amazes me that this method fails so strongly even after trying different parameters set and original author's GUI in Qt.

Also, is there some alternative in `open3d` that is planned?

Thanks.

Best regards,
Valeria