Serialize core output into data to send to server

[moreirathomas]

The output of the core must be serialized into a data structure posted to the server.

  "request": {
    "url": "",
    "method": "",
    "body": {},
    "headers": [],
    "queryParams": []
  },
  "args": {
    "requestPerSecond": 10,
    "requestsCount": 100,
    "totalTimeout": 1000,
    "requestTimeout": 800
  },
  "metadata": {
    "id": "",
    "date": "",
    "collection": "",
    "label": ""
    "tag": "",
  },
  "results": {
    "totalTime": 100,
    "responses": [
      {
        "status": 200,
        "time": 100
      }
    ]
  }