create example that shows variation of plasma parameters (shape, density, temp) on neutronics outputs.

[shimwell]

This requires the parametric plasma source to be fully working

Currently there are a few open PR on the plasma source repo that are planning to fix the issue

https://github.com/open-radiation-sources/parametric-plasma-source/pull/16

https://github.com/open-radiation-sources/parametric-plasma-source/pull/19