Alert specific for each permutation of a sentry tag

### Problem Statement

In Sentry alerts, I can set an individual alert based on filters such as tag, message, etc. However, I want to set up an alarm that essentially says "alert me if issue X happens for any respective tag value more than 10 times in 5 minutes".

To help illustrate, an example might be that you send a sentry warning when a rate limit `429` occurs. For this error, you have a sentry tag for the customer name. Let's say I have customer A, B, & C. I want to be alerted if customer A is rate limited more than 10 times in 5 minutes. Same, respectively, for B & C.

Right now in sentry, I would have to go make 3 different alerts for each enumeration of customer tag. This does not scale well.

### Solution Brainstorm

_No response_

### Product Area

Alerts

Start with the Alerts product area and review how alert filters and tag values are currently represented. Use the customer A/B/C example to define the expected per-tag threshold behavior, then identify the relevant alerting tests or entry points. Done means one alert can independently evaluate the threshold for each tag value without manually creating an alert per value.

Written by the indexing model from the issue text.