IoT Hub supports new Azure Monitor metric alerts

We've added Azure IoT Hub support for the [newer Azure Monitor metric alerts](https://docs.microsoft.com/azure/azure-monitor/platform/alerts-metric-overview). These new metric alerts are faster and more flexible than the older classic alerts, and they’re easier to set up. To get started: 1. Go to your IoT hub in the Azure portal. 2. Under **Monitoring**, select **Alerts**. 3. Select **New alert rule**. 4. Select **Add condition**. Notice that **Metrics**is now a supported signal type. 5. Follow prompts to finish setting up the alert. We’ve also fixed a bug with device count metrics in IoT Hub, specifically `connectedDeviceCount` and `totalDeviceCount`, where they don’t correctly trigger with classic alerts. They now work properly with the new alerts. As such, we’ll remove the deprecated device count metrics (`devices.totalDevices` and `devices.connectedDevices.allProtocol`) in September 2019\. To see which metrics you can set up alerts for, go to [IoT Hub metrics](https://docs.microsoft.com/azure/iot-hub/iot-hub-metrics). * Azure IoT Hub * Azure Monitor * Features * Retirements * [ Azure IoT Hub](https://azure.microsoft.com/en-gb/products/iot-hub/) * [ Azure Monitor](https://azure.microsoft.com/en-gb/services/monitor/)