message: IoTHub: adding new routing source into 2021-07-01-preview
diff: "DeviceLifecycleEvents",
  "DeviceJobLifecycleEvents",
  "DigitalTwinChangeEvents",
  - "DeviceConnectionStateEvents"
  + "DeviceConnectionStateEvents",
  + "MqttBrokerMessages"
  ],
  "type": "string",
  "x-ms-enum": {
  "DeviceLifecycleEvents",
  "DeviceJobLifecycleEvents",
  "DigitalTwinChangeEvents",
  - "DeviceConnectionStateEvents"
  + "DeviceConnectionStateEvents",
  + "MqttBrokerMessages"
  ],
  "type": "string",
  "x-ms-enum": {
  