Flexible Release-Based Alert Filtering

### Problem Statement

It would be helpful to have more flexible options for filtering alerts based on release recency. Today, alerts can only target the single “latest release,” which makes it difficult to focus on a meaningful window of recent activity, especially for teams that deploy frequently.

Ideally, users should be able to define alert conditions like “releases from the last X days” or “last N releases.”

It would also be valuable to extend this capability across both issue alerts and metric alerts, and to support additional release attributes like release stage (e.g., adopted).

### Solution Brainstorm

_No response_

### Product Area

Alerts

Start in the Alerts product area by tracing how the existing single “latest release” filter is represented for issue and metric alerts. Clarify the intended semantics for time windows, release counts, and release stages, then define completion around supporting those options consistently across both alert types.

Written by the indexing model from the issue text.