Alerts - Have a When trigger that looks for when ownership Change to team X to send out slack alert to Team X

### Problem Statement

When Team A is the overseeing team responsible for some stack frames across multiple projects they want to be alerted in Slack when the project's teams assign the issues to Team A.

The re-assigning happens after the issue is being created and it should not fire everytime a event gets into an existing issue as that would create noise.

### Solution Brainstorm

When Ownership changes on Issue A and this ownership is Team A there needs to be an alert that fires to the Slack channel of Team A.
Everything is in place already except the "When ownership changes to Team X" trigger

### Product Area

Alerts

┆Issue is synchronized with this [Jira Improvement](https://getsentry.atlassian.net/browse/FEEDBACK-2368) by [Unito](https://www.unito.io)

Start by tracing the existing alert triggers and the ownership-change handling described in the issue. Verify how a change to Team X can be distinguished from later events on the same issue, then confirm the Slack notification path for that team. Done means a change of ownership to a team sends that team's Slack alert without notifying again for subsequent events.

Written by the indexing model from the issue text.