message: Update swagger-extensions.json
  Adding missing items
diff: "x-nullable": {
  "$ref": "#/definitions/xNullable"
  },
  + "x-ms-header-collection-prefix": {
  + "type": "string",
  + "description": "Provides the ability to specify a key value mapping, using given prefix as the prefix of all keys."
  + },
  "x-ms-client-name": {
  "type": "string",
  "description": "A code-generator-friendly name for the header."
  "type": "string",
  "description": "A code-generator-friendly name for the parameter."
  },
  + "x-ms-header-collection-prefix": {
  + "type": "string",
  + "description": "Provides the ability to specify a key value mapping, using given prefix as the prefix of all keys."
  + },
  "x-ms-client-request-id": {
  "$ref": "#/definitions/xmsClientRequestId"
  },
  