[TASK] UX enhancement for EXT:documentation

Rework the documentation module according to the
discussion with the TYPO3 Usability Team.

Resolves: #54067
Releases: 6.2
Change-Id: Ia59c9a1554080b71412b467f6621bc7270a81c72
Reviewed-on: https://review.typo3.org/25975
Reviewed-by: Markus Klein
Tested-by: Markus Klein
Reviewed-by: Xavier Perseguers
Tested-by: Xavier Perseguers