Support stacked histograms

[maximlt]

This was first requested in holoviz/hvplot#483 (comment), HoloViews could add support to stacked histograms.

Plotly supports that for instance:

[tupui]

This could help others, I also asked on the forum and here is a recipe to workaround:

https://discourse.holoviz.org/t/stacked-histogram/6205