[FEATURE] Migrate sysext manuals to reST

All system extension manuals are migrated to reStructured Text.
All OpenOffice manuals are removed.

Resolves: #50052
Releases: 6.2
Change-Id: I9d8d9ad433276e6105d9c38b9f2a3b34dc8749f6
Reviewed-on: https://review.typo3.org/22337
Tested-by: Wouter Wolters
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn
Reviewed-by: Georg Ringer
Tested-by: Georg Ringer