Support Alerting for PromQL Charts #3113

Currently, HyperDX supports setting up alerts on various chart types, but the "Alert" configuration tab is disabled when using PromQL charts. Users who rely heavily on Prometheus metrics need a way to trigger notifications based on PromQL query evaluations natively within HyperDX, rather than relying on external Alertmanagers.

Solution

Enable the alert configuration interface for PromQL charts and evaluate these alerts in the backend checkAlerts task loop.

Specifically:

1. Allow users to configure thresholds, evaluation windows, and notification channels for PromQL charts exactly as they do for standard charts.
2. During the background evaluation loop, proxy these queries to the underlying Prometheus endpoint or through ClickHouse's prometheusQueryRange function.
3. Integrate the results into the standard alert state management and notification pipeline.

Additional Context

• The backend already supports querying Prometheus endpoints for standard dashboard views, we just need to route background alert evaluations through the same mechanisms.
• Requires unblocking PromqlSavedChartConfig in the AlertChartConfigSchema.