Grafana 12 requires explicit relativeTimeRange on all alert rule data
queries. Without it, queries default to {from: 0, to: 0} which is
rejected as invalid, causing Grafana to crash on startup during
alerting provisioning.
Added relativeTimeRange to all data entries:
- Prometheus queries: {from: 600, to: 0} (10 min lookback)
- Expression refs: {from: 0, to: 0}
This was preventing Grafana from starting on london-a, which meant
alerts (including Host Down for copenhagen-a) could never auto-resolve.