Add more advanced example notebooks

[flferretti]

As the library starts to have more users, the need for a more complete documentation and examples naturally emerges, as seen in #175 and #187. For this reason, this issue aims at showing more than the basics JaxSim features already presented in the existing notebooks.

The idea is both to improve the existing examples by simplifying the visualisation logic when using headless rendering and to add one or more notebooks with more advanced use-cases using e.g. reinforcement learning or model-based control architectures.

[diegoferigo]

Having more examples that are automatically tested in CI would be great (and in our case, after #187, readthedocs would fail to render if a notebook is not running). I have some very old examples from late 2021 that were quite nice. Nothing fancy, just simple simulations, but there were a nice showcase of the simulation potential. Now that we can render them in our documentation, it's probably worth bringing them back. We can talk about this f2f.