[TASK] Move documentation to reST

Move documentation to reStructuredText and remove
old formats.

Resolves: #58360
Releases: 2.3
Change-Id: I5f53f01f05e231dfdf14040c9eaf94b01eeada44
Reviewed-on: https://review.typo3.org/29786
Reviewed-by: Francois Suter
Tested-by: Francois Suter