Restructure pages docs
Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/28688
Depends on https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/9583
cc/ @axil @SeanPackham @markpundsack for feedback pls :)
Do not update/delete: Banner broadcast message test data
Do not update/delete: Notification broadcast message test data
Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/28688
Depends on https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/9583
cc/ @axil @SeanPackham @markpundsack for feedback pls :)