Update rake task, add subtype label

Updates lib/tasks/redirects.rake to include the maintenancerefactor subtype label. I have one other idea, but I'll have to leave it as an optional comment because I don't know how to do it.

Related links

• Related to Docs project maintenance tasks - September 2022 (technical-writing#675 - closed)
• All auto-generated cleanup MRs for this month:
  • Related to Clean up docs redirects - 2022-09-29 (gitlab!99282 - merged)
  • Related to Clean up docs redirects - 2022-09-29 (omnibus-gitlab!6403 - merged)
  • Related to Clean up docs redirects - 2022-09-29 (gitlab-runner!3632 - merged)
  • Related to Clean up docs redirects - 2022-09-29 (!3137 - merged)