Require that all sev2 and sev1 user-facing incidents have service, rootcase and correctiveaction labels

As a followup to the discussion in mstaff#189 (comment 1329026770), I suggest that if a user-facing sev2 or sev1 incident goes x days (7?) without any activity and without a linked corrective action, we mention the DRI until a corrective action is added, or a special label is added NoCorrectiveActionNeeded.

In addition to corrective actions, I suggest we expand this to our required labels

Proposal

• Clarify section on required labels gitlab-com/www-gitlab-com!126420 (merged)
• Create Triage-ops Rule that adds a note with DRI mention (plus others) if a Needed label is present for N days. triage-ops!191 (merged)