Keep logs in a file

[hector-js]

Is your feature request related to a problem? Please describe.
At this moment, we dont have any logs or any place where we can save the story of the requests.

Describe the solution you'd like
Record all the request in a logs-{timestamp}.json file under logs folder

{
  `${method}${path}${scenario_number}`:{
             time: '${timestamp}',
             _req:{
                 ...
             },
             _res: {
                 ...
             }                                                          
    },
    ...
}