[Bugfix] Add Index on sys_domain

TYPO3 checks if a redirect is needed for a domain by issuing a
select on sys_domain. In the where clause the columns redirectTo
and hidden are used. These columns have no index, thus the
select is slow.

This patch adds the combined key to the sql definition.

Resolves: #55181
Releases: 6.2
Change-Id: I7d7463e0d3e6abb53c4b0fccf205e4b1eb867878
Reviewed-on: https://review.typo3.org/27167
Reviewed-by: Anja Leichsenring
Tested-by: Anja Leichsenring
Reviewed-by: Benjamin Mack
Tested-by: Benjamin Mack