Adding contour lines

[shimwell]

It would be helpful to be able to add contour lines

perhaps the user could specify a list of mesh values to plot as contour lines.

[shimwell]

example of plotly contour lines

https://github.com/fusion-energy/neutronics-workshop/blob/cd9a0d833bffd20698f974c64f44b822ba6306cb/tasks/task_13_parameter_study_sampling/plotting_tools.py#L102-L136