Extend template visualization functionality: normalization systematics and post-fit effects

[alexander-held]

Discussed in https://github.com/scikit-hep/cabinetry/discussions/472

^{Originally posted by Tomoya-Iizawa April 19, 2024} I think cabinetry.visualize.templates produces plots for shape uncertainties and not for normalization uncertainties. Is there any way to produce plots to show the impact of the normalization uncertainties?

And this function shows the pre-fit distribution of the variation samples, right? If so, is there any way to show the post-fit?

Best, Tomoya