Merge branch 'wiki-404' into 'master'

Add the proper empty state when wiki page not found

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/156003



Merged-by: Lorenz van Herwaarden <lvanherwaarden@gitlab.com>
Approved-by: Annabel Dunstone Gray <annabel.dunstone@gmail.com>
Approved-by: Himanshu Kapoor <info@fleon.org>
Reviewed-by: Annabel Dunstone Gray <annabel.dunstone@gmail.com>
Co-authored-by: Julia Miocene <jmiocene@gitlab.com>