[TASK] Move documentation to reST

Move documentation to reStructuredText.
Removed old documentation.

Resolves: #58402
Releases: 1.6
Change-Id: Idc6175f4e40b5fe79fe99f36de7de08dffaf9f46
Reviewed-on: https://review.typo3.org/30546
Reviewed-by: Francois Suter
Tested-by: Francois Suter