Fix NetworkSwitch perturbation tutorial

[rodrigomha]

We need to explicitly state to use using PowerNetworkMatrices when creating Ybus.

In addition, we should discuss if NetworkSwitch should ONLY use a SparseMatrix or not. From a user perspective we should allow the user to use directly a dense matrix if they want.

In any case, we need to update the tutorial of Perturbations since it is using Dense Matrices: https://nrel-sienna.github.io/PowerSimulationsDynamics.jl/stable/perturbations/

[jd-lara]

I don't think this is a bug. We have always assumed that the user would pass a Bus object which is by default sparse.