message: add clientData properties to data migration tasks
diff: "$ref": "./Commands.json#/definitions/CommandProperties"
  },
  "readOnly": true
  + },
  + "clientData": {
  + "type": "object",
  + "description": "Key value pairs of client data to attach meta data information to task",
  + "additionalProperties": {
  + "type": "string"
  + }
  }
  },
  "required": [ "taskType" ],
  