[Feature Request] Cancelled Rate for Metrics Alerts

### Problem Statement

Hi, I'm using Sentry Performance for mobile app.
ok, cancel, unknown, unknownError status does not counts as failure rate.
document: https://docs.sentry.io/product/performance/metrics/#failure-rate

Therefore, if either cancel, uknown, unknownError has spike in application, there are no way detect this problem as alert.

I really need alert for cancelled status rate.
(if there are any solution for this in current feature, please let me know.)
In addition, in the future, it is really nice to have feature creating rate alert for each status.

### Solution Brainstorm

_No response_

### Product Area

Alerts