[BUGFIX] Show default site name in installation wizard

Currently in step 4 the input box for the site name is empty. This patch
re-adds the default site name from FactoryConfiguration.php as initial
value.

Resolves: #82876
Releases: master
Change-Id: I391254cf7ae6e5f8aa45003035aebaf513e733d3
Reviewed-on: https://review.typo3.org/54490


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: Benni Mack <benni@typo3.org>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: Wouter Wolters <typo3@wouterwolters.nl>