Add 'Data flows' section to IoT operations TOC

Author: vadim-kovalyov

articles/iot-operations/toc.yml

@@ -393,6 +393,9 @@ items:
               - name: MQTT broker
                 href: reference/observability-metrics-mqtt-broker.md
                 displayName: metrics, observability
+              - name: Data flows
+                href: reference/observability-metrics-data-flows.md
+                displayName: metrics, observability
               - name: Connector for OPC UA
                 href: reference/observability-metrics-opcua-broker.md
                 displayName: metrics, observability