Enable RevertMrTemplateNudger and restrict to canonical project

What does this MR do and why?

Follow-up MR of !1836 (merged).

• Remove the sandbox: true from RevertMrTemplateNudger
• Restrict the processor from gitlab-org to gitlab-org/gitlab, as the Revert MR template is only defined inside the canonical project.

Does the processor work?

• Revert MR without the Revert MR template: https://gitlab.com/gitlab-org/quality/engineering-productivity/triage-ops-playground/-/merge_requests/2
  • ✅ We get the nudge for using the template
• Revert MR with the Revert MR template: https://gitlab.com/gitlab-org/quality/engineering-productivity/triage-ops-playground/-/merge_requests/3
  • ✅ We get no nudges
• Regular MR with the Revert MR template: https://gitlab.com/gitlab-org/quality/engineering-productivity/triage-ops-playground/-/merge_requests/4
  • ✅ We get a warning that this cannot be done

Expected impact & dry-runs

These are strongly recommended to assist reviewers and reduce the time to merge your change.

See https://gitlab.com/gitlab-org/quality/triage-ops/-/tree/master/doc/scheduled#testing-with-a-dry-run on how to perform dry-runs.

Action items

• (If applicable) Add documentation to the handbook pages for Triage Operations =>
• (If applicable) Identify the affected groups and how to communicate to them:
  • /cc @person_or_group =>
  • Relevant Slack channels =>
  • Engineering week-in-review

Message for EWIR

[Maintainers] @ddieulivol: We now have a revert MR template that will allow you to speed up revert MRs by applying appropriate labels (see the docs). We also introduced a reminder for revert MRs that didn't use the template (see !1836 (merged)) to tell people about the revert MR template.