[TASK] Move documentation to reST

Move documentation to reStructuredText.
Remove old format.

Resolves: #57777
Releases: 1.5
Change-Id: I8668f52621530753a66f449f6e75e6927bc646af
Reviewed-on: https://review.typo3.org/29330
Reviewed-by: Francois Suter
Tested-by: Francois Suter