gitlab: Enable domain-level redirects feature flag for Pages

This feature is needed for the static copy of bugs.a.o[2], to redirect
some of the migrated tasks to the new gitlab URLs.

[1] https://docs.gitlab.com/ee/user/project/pages/redirects.html#domain-level-redirects
[2] https://gitlab.archlinux.org/archlinux/bugs-archive/-/blob/snapshots/_redirects