gitlab: Use the legacy storage[1] for GitLab Pages

gitlab-pages uses the API source by default now[2] but DNS resolution is
broken[3] so we need to use the disk config source.
Reported upstream here[4].

[1] https://docs.gitlab.com/ee/administration/pages/#gitlab-pages-doesnt-work-after-upgrading-to-gitlab-140-or-above
[2] https://gitlab.com/gitlab-org/gitlab-pages/-/commit/9a30f40a785ffe586a79a75ebebabda5f513b76f
[3] https://gitlab.com/gitlab-org/omnibus-gitlab/-/issues/4243
[4] https://gitlab.com/gitlab-org/gitlab/-/issues/331699#note_608473496