[ReleasePR iothub] [Hub Generated] Review request for Microsoft.Devices to add version preview/2021-09-01-preview (#1858)

Create to sync Azure/azure-rest-api-specs#15428
[ReCreate this PR](https://github.com/azure-resource-manager-schemas/compare/main...AzureSDKAutomation:sdkAuto/iothub?expand=1)

Author: msftbot[bot]

schemas/2021-07-01-preview/Microsoft.Devices.json

@@ -459,7 +459,8 @@
                 "DeviceLifecycleEvents",
                 "DeviceJobLifecycleEvents",
                 "DigitalTwinChangeEvents",
-                "DeviceConnectionStateEvents"
+                "DeviceConnectionStateEvents",
+                "MqttBrokerMessages"
               ]
             },
             {
@@ -1228,7 +1229,8 @@
                 "DeviceLifecycleEvents",
                 "DeviceJobLifecycleEvents",
                 "DigitalTwinChangeEvents",
-                "DeviceConnectionStateEvents"
+                "DeviceConnectionStateEvents",
+                "MqttBrokerMessages"
               ]
             },
             {