Add a tutorial for the frustum_visual example

A [FrustumVisual](https://github.com/gazebosim/gz-rendering/blob/gz-rendering9/include/gz/rendering/FrustumVisual.hh) class was added in https://github.com/gazebosim/gz-rendering/pull/1095 for visualizing the frustum of camera sensors. An example exists in [examples/frustum_visual]( https://github.com/gazebosim/gz-rendering/tree/gz-rendering9/examples/frustum_visual). We should add a tutorial explaining the example, very much like other tutorials in the [tutorials](https://github.com/gazebosim/gz-rendering/tree/gz-rendering9/tutorials) dir.

## Implementation suggestion

1. Add a frustum visual tutorial in the tutorials directory
1. In the tutorial, provide steps for building the example, and the expected output (screenshot).
1. Add explanations for the code, specifically for the [API calls](https://github.com/gazebosim/gz-rendering/blob/597d8892d7478b89f7f794c176f737578dd9c40a/examples/frustum_visual/Main.cc#L103-L106) needed to construct a FrustumVisual.
1. Once done, the tutorial needs to be added to [tutorials.md.in](https://github.com/gazebosim/gz-rendering/blob/main/tutorials.md.in)

See other tutorials in the tutorials directory for reference. These tutorials should be fairly straightforwad.