[BUGFIX] Add index to table pages

To detects the siteroot by querying the pages table with the
columns deleted, hidden, is_siteroot. This patch introduces
a combined index on those colums

Resolves: #55180
Releases: 6.2
Change-Id: Icae63670419cf9bc0029e2aa570cdf0108b9d62a
Reviewed-on: https://review.typo3.org/27154
Reviewed-by: Anja Leichsenring
Tested-by: Anja Leichsenring
Reviewed-by: Marcin Sągol
Reviewed-by: Benjamin Mack
Tested-by: Benjamin Mack