The `gitlab.checkConfig.objectStorage.pages.configured` check required a
per-Pages `connection` whenever Pages and its object storage were enabled,
regardless of whether consolidated object storage was in use. In
consolidated mode Pages inherits the shared `object_store.connection` and
its per-Pages connection is never rendered, so a valid default setup was
incorrectly failing the install with a request to configure a connection
that the templates ignore.

Guard the check so a per-Pages connection is only required when
consolidated object storage is disabled. Also extend the consolidated
mixing detection to flag `global.pages.objectStore.connection` (and an
empty bucket), matching how the other object storage types are validated,
so a silently-ignored Pages connection no longer slips through.

Update the test defaults to drop the now-unnecessary Pages connection (which
would otherwise trip the new mixing detection) and add specs covering both
the consolidated and type-specific branches.

Closes: #6531

Changelog: fixed

Backport 10.1: Pages object storage validation fixes

See merge request !5138



Merged-by: João Alexandre Cunha <j.a.cunha@gmail.com>
Approved-by: Stefan Bordei <sbordei@gitlab.com>
Approved-by: João Alexandre Cunha <j.a.cunha@gmail.com>
Co-authored-by: Lucas Li <lli@gitlab.com>

[ci skip]

[ci skip]