Feature request: Data warehouse sources - add native alerting for sync failures

Feature request

Is your feature request related to a problem?

Data warehouse source syncs (Redshift, Postgres, etc.) for analysis have no method for alerts/notifications when a sync fails, or when data becomes stale. Currently, the only way to discover a failed sync is to log in and check the project's /health page.

Describe the solution you'd like

Native alerting for data warehouse source sync health. This could include:

• Notifications (Slack, email, webhook) when a sync job fails or enters an error state
• Notifications when a sync hasn't completed within a configurable freshness window
• Optionally, surfacing sync status in the existing Alerts system (e.g., extending Alerts beyond Trends insights to cover sync health)

Describe alternatives you've considered

• Polling the /api/environments/{id}/external_data_sources/{id}/jobs/ endpoint programmatically and building an external monitor
• Creating a Trends insight that tracks recent row counts from synced tables and setting an alert on it as a data-freshness proxy
• Manual inspection of the Sources UI after each expected sync window

(each of these add maintenance overhead)

Additional context

From: https://posthoghelp.zendesk.com/agent/tickets/57837 (moved to PostHog: https://us.posthog.com/project/2/support/tickets/59921)

Debug info

Start by reviewing the existing /health page, Sources UI, Alerts system, and the /api/environments/{id}/external_data_sources/{id}/jobs/ endpoint mentioned in the issue. Define the supported sync failure and freshness states, notification targets, and configuration boundaries before implementation. Done means users can receive native alerts for failed or stale data warehouse syncs without manual polling.