improve RNA-seq example app setup

[donyunardi]

I would recommend opening a question in teal.gallery for RNA-seq app and discuss: is it possible to select hd2 experiment as a default used on Forestplot? The current default one hd1 has this message displayed No assays eligible for this experiment, please make sure to add normalized assays

https://github.com/insightsengineering/teal.slice/issues/526#issuecomment-1916496507