message: export open api as json document
diff: "swagger-link",
  "wadl-link",
  "wsdl-link",
  - "openapi-link"
  + "openapi-link",
  + "openapi+json-link"
  ],
  "x-ms-enum": {
  "name": "ExportFormat",
  "value": "openapi-link",
  "description": "Export the Api Definition in OpenApi Specification 3.0 to Storage Blob.",
  "name": "Openapi"
  + },
  + {
  + "value": "openapi+json-link",
  + "description": "Export the Api Definition in OpenApi Specification 3.0 as JSON document to Storage Blob.",
  + "name": "OpenapiJson"
  }
  ]
  },
  