IoTHub: adding new routing source into 2021-07-01-preview (Azure#15398)

Co-authored-by: vfedonkin <[email protected]>

Author: vfedonkin

specification/iothub/resource-manager/Microsoft.Devices/preview/2021-07-01-preview/iothub.json

@@ -3181,7 +3181,8 @@
             "DeviceLifecycleEvents",
             "DeviceJobLifecycleEvents",
             "DigitalTwinChangeEvents",
-            "DeviceConnectionStateEvents"
+            "DeviceConnectionStateEvents",
+            "MqttBrokerMessages"
           ],
           "type": "string",
           "x-ms-enum": {
@@ -3970,7 +3971,8 @@
             "DeviceLifecycleEvents",
             "DeviceJobLifecycleEvents",
             "DigitalTwinChangeEvents",
-            "DeviceConnectionStateEvents"
+            "DeviceConnectionStateEvents",
+            "MqttBrokerMessages"
           ],
           "type": "string",
           "x-ms-enum": {