Add voltage profile plotting

[alihamdan]

Resolves #298

[alihamdan]

Examples in the documentation: https://roseau-load-flow--429.org.readthedocs.build/en/429/usage/Plotting.html

Here are some other examples using the network "24_MVFeeder0277" from https://github.com/RoseauTechnologies/Representative_French_Power_Grids:

1. Plotting only the MV level -- no transformer traversal (default):

   rlf.plotting.voltage_profile(en, mode="min").plot_plotly()

   

2. Plotting the entire network -- traversing transformers:

   rlf.plotting.voltage_profile(en, mode="min", traverse_transformers=True).plot_plotly()

   

3. Plotting the LV network of transformer "24_MVLV52158" -- selecting the starting bus:

   rlf.plotting.voltage_profile(
       en, mode="min", starting_bus_id="24_MVLV52158_LV", distance_unit="m"
   ).plot_plotly()

   

[alihamdan]

I'll merge this now and follow up later if @Saelyos has any concerns/suggestions when he gets back to office