Novelty Alerts for New Failures Only

Problem: Current alerting options can be noisy when large numbers of stacks fail with the same issue.
Request:
Introduce optional novelty-based alerts — notify teams only when a new failure pattern is detected (i.e., something that hasn’t been seen before in the current window).
Impact: Reduces alert fatigue while still catching regressions early. Similar logic used in tools like Sentry for new exceptions.