[BUGFIX] Add default values from setup.txt and raise override to 20

Update the indexed_search extension documentation with
proper TypoScript values for overriding templates.

Resolves: #79006
Releases: master, 7.6

Change-Id: Ie034d6b192675fa1a453622b90296d39c80d2447
Reviewed-on: https://review.typo3.org/50977


Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Stephan Großberndt <stephan@grossberndt.de>
Reviewed-by: Mathias Schreiber <mathias.schreiber@wmdb.de>
Tested-by: Mathias Schreiber <mathias.schreiber@wmdb.de>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: Wouter Wolters <typo3@wouterwolters.nl>