[DOCS] Update TypoScript documentation of Indexed Search

To update the Indexed Search TypoScript documentation the following tasks
 have been completed:

* Use of `..  confval::` block
* All available settings are named
* Some description texts have been optimized
* Code examples were created
* Indentation was done with 4 spaces
* Heading types were corrected
* Default values were entered separately outside the body text
* Missing references were corrected

Releases: main, 11.5
Resolves: #99353
Resolves: #99379
Change-Id: Ice6c38607fed68347dc38617c7dea8634f073483
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/77214


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