Alerts for queue monitoring metrics

### Problem Statement Sentry's queue monitoring provides valuable metrics like average time in queue and average processing time, but currently doesn't support alerting based on these metrics. This creates a reactive monitoring approach where performance degradation goes unnoticed until manual dashboard checks or user complaints occur, leading to delayed incident response and potential user impact. ### Solution Brainstorm Add alert rule capabilities for queue monitoring metrics, allowing users to: - Set thresholds for average queue time and processing time - Support both absolute thresholds and percentage-based changes over time periods This would enable proactive monitoring and faster incident detection for queue-related performance issues. ### Product Area Alerts