Suggest openxlsx2 instead of openxlsx

[olivroy]

Opening this PR for discussion.

Since openxlsx2 is actively maintained, a bit easier to use, and closer to the tidyverse.

See this blog post for an example. https://rdiscovery.netlify.app/posts/2023-11-11_openxlsx2/

If you decide to move along with this, I will be happy to update the solution to exercice.