message: Add identity property to service resource
diff: "etag": {
  "description": "An etag associated with the resource, used for optimistic concurrency when editing it.",
  "type": "string"
  + },
  + "identity": {
  + "type": "object",
  + "description": "Setting indicating whether the service has a managed identity associated with it.",
  + "properties": {
  + "type":{
  + "description" : "Type of identity being specified, currently SystemAssigned and None are allowed.",
  + "type": "string",
  + "enum": [
  + "SystemAssigned",
  + "None"
  + ],
  + "x-ms-enum": {
  + "name": "ManagedServiceIdentityType",
  + "modelAsString": true
  + }
  + }
  + }
  }
  },
  "x-ms-azure-resource": true,
  