[Release Issue] Improve Dependabot Alert performance, stability, and scalability with db cluster improvements [GA]

### Value Prop

Dependabot alerts are a critical line of defense for identifying vulnerable dependencies across your repositories. As the volume of advisories and monitored repositories continues to grow at unprecedented scale, customers need alerts that load quickly and remain reliable — without delays or timeouts. These database cluster improvements ensure that Dependabot alerts stay fast and responsive, so developers can triage and remediate vulnerabilities without friction, even as their organizations scale.

### Expected Outcome

We expect customers to experience consistently fast load times and improved reliability when viewing and managing Dependabot alerts. By optimizing data retention and the underlying database infrastructure, we eliminate performance bottlenecks that can surface as alert pages slow to load or fail under heavy usage. The result is a more stable, scalable alerting experience that keeps pace with the growing volume of security advisories — giving security and engineering teams confidence that they can act on vulnerabilities promptly across all of their repositories.