[DOCS] Rework lowlevel documentation

- Move the content from the README.rst into the Documentation folder.
- The README.rst now defaults to the content of the other system extensions.
- Describe all modules
- Describe available configuration options (user TSconfig)
- Provide automatic screenshots
- Align to the new documentation standards (https://docs.typo3.org/m/typo3/docs-how-to-document/main/en-us/GeneralConventions/FileStructure.html)

Resolves: #95886
Releases: main
Change-Id: Iad905b23e53be47ae3f107f9b454dbdb15780cef
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/72068


Tested-by: core-ci <typo3@b13.com>
Tested-by: Benni Mack <benni@typo3.org>
Tested-by: Lina Wolf <112@linawolf.de>
Reviewed-by: Benni Mack <benni@typo3.org>
Reviewed-by: Lina Wolf <112@linawolf.de>