[Datadog] Forecast-Based Warning (Predictive Alerting)

The forecast() function predicts where a metric will be in the future based on past behavior. Elastic requires the "Forecasting" feature within their ML module, which isn't a simple JSON query string—it's a separate stateful job.

```json
{
"name": "Predictive Disk Space Exhaustion",
"type": "query alert",
"query": "avg(last_1h):forecast(avg:system.disk.used{host:db-master}, 'linear', 3, interval='60s', history='7d') >= 0.95",
"message": "Disk is predicted to hit 95% capacity within the next 3 hours. @dba",
"options": {
"thresholds": { "critical": 1 }
}
}
```