[FEATURE] Show extension keys in documentation list

Show extension keys in the lists as well.

Resolves: #52782
Releases: 6.2
Change-Id: Idf3d4e4eb1595866de4196c3d71b65619b2031d3
Reviewed-on: https://review.typo3.org/24731
Reviewed-by: Xavier Perseguers
Tested-by: Xavier Perseguers
Reviewed-by: Nicole Cordes
Tested-by: Nicole Cordes
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters