Migrate the `bug`, `feature`, and `backstage` labels to be scoped labels

Part of https://gitlab.com/gitlab-org/gitlab-ce/issues/60166.

The idea is to migrate:

1. ~bug to typebug

2. ~feature to typefeature

3. ~backstage to ~"type::backstage" TODO:

4. Prepare a MR for https://gitlab.com/gitlab-org/gitlab-ce: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/29563

5. Prepare a MR for https://gitlab.com/gitlab-org/quality/triage-ops: gitlab-org/quality/triage-ops!150 (closed)

6. Prepare a MR for https://gitlab.com/gitlab-org/gitlab-insights: gitlab-insights!114 (closed)

7. Prepare a MR for https://gitlab.com/DylanGriffith/knative-bots/blob/master/lib/throughput_labels.rb

8. Prepare a MR for https://gitlab.com/gitlab-com/www-gitlab-com: gitlab-com/www-gitlab-com!24219 (closed)

9. Change the group labels

10. Announce it on Slack and team call