[FIX] website_slides: improve documentation course layout and not fullscreen lesson page

Purpose of this commit is to perform a cleaning of

 * documentation course: add a new specific navigation for documentation
   course with a sort option and filters on slide types; clean overall layout
   of documentation course to have a better-looking result as this page was
   still not really updated;
 * lesson not fullscreen page: global layout and cleaning of not-fullscreen
   page to have a better-looking result. Notably related slides for
   documentation slide is set on right, and some UX bits are tweakes;

Commit linked to task ID 1941250 and PR #31977