improve RNA-seq example app setup

> 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

Start by locating the RNA-seq example app setup and how its default experiment is selected. Review the linked teal.slice discussion about using hd2 instead of hd1; done should mean the example opens with a default experiment that has eligible normalized assays and does not display the current error.

Written by the indexing model from the issue text.