Multi-region event ingestion

The workspace sync service was extended to publish events to multiple event streams in parallel.

1. Independent event streams can now be configured side-by-side, enabling multi-region delivery.
2. Each downstream consumer in the Data pipeline can pick which stream it consumes from.
3. Enables active/active analytics across regions and lets us drain one region during maintenance without losing events.
4. Events are now tagged with their publishing region for routing and observability.