Switch to gitlab_rails['auto_migrate'] = false
What does this MR do?
Update docs to use gitlab_rails['auto_migrate'] = false rather than /etc/gitlab/skip-auto-migrations per https://gitlab.com/gitlab-org/omnibus-gitlab/issues/1685#note_17823027.
Do not update/delete: Banner broadcast message test data
Do not update/delete: Notification broadcast message test data
Update docs to use gitlab_rails['auto_migrate'] = false rather than /etc/gitlab/skip-auto-migrations per https://gitlab.com/gitlab-org/omnibus-gitlab/issues/1685#note_17823027.