Get alerted when a release contains a certain number of new unique issues (not a certain number of events)

### Problem Statement

Opening on behalf of a customer, who wrote

> If we do a new release where XYZ people contributed to that release, we want to look at those new releases, and say "Hey this one has over 20 new issues so alert the teams that were a part of that release that they need to go look why it has so many new issues."

As far as I know, this is not currently possible (although there are plenty of ways to alert based on volume of errors, or users experiencing errors within a release).

### Solution Brainstorm

Add the ability to alert when a release exceeds a certain threshold of new unique issues.

### Product Area

Alerts

The issue names only the Alerts product area and does not mention files, tests, or entry points. Start by surveying existing alerting and release-related paths; done means an alert can trigger when a release exceeds a configured threshold of new unique issues and notify the relevant teams.

Written by the indexing model from the issue text.