adda facet plot to link in viz lesson

[mistrm82]

pseudbulk DE lesson has code for a nice facet gene plot of expression differences between groups. Add in here

[Gammerdinger]

In this lesson: https://hbctraining.github.io/Intro-to-DGE-Quarto/lessons/12_DGE_visualizing_results.html

We link out to this aside which does the top 20 genes but it isn't faceted: https://hbctraining.github.io/Intro-to-DGE-Quarto/lessons/Aside_top20_genes-expression_plotting.html

Can we go like the top 6 and facet it like this: https://hbctraining.github.io/Pseudobulk-for-scRNAseq-Quarto/lessons/08_pseudobulk_DE_visualizations.html