automate R version prereq for learners setup

[avallecam]

I see a couple of options:

• Make a script used internally to determine the minimum required R version to use the different packages from the lesson.
• Stick with the tidyverse policy, which is what our packages are using: 5 last minor versions of R are ok. These versions can be displayed automatically via the rversions package.
• Move away from the "required" phrasing but say something like "this lesson has been developed and tested with R version XXXX. Please ensure you have a recent version of R installed.". The R version could be extracted from renv.lock.

Originally posted by @Bisaloo in #102 (comment)