[Docs] Add application examples

[awennersteen]

What is the expected enhancement?

We should port at least 2 of

https://pulser.readthedocs.io/en/stable/tutorials/optimization.html
https://pulser.readthedocs.io/en/stable/tutorials/qubo.html
https://pulser.readthedocs.io/en/stable/tutorials/mwis.html

I would just use the local QuTiP backend I personally.