adapter for grape-batch request

We are using [grape-batch](https://github.com/c4mprod/grape-batch) to handle batch requests in the server.

a POST http request is expected with a body like:

```
{
  requests: 
    [
      {
        method: 'GET', 
        path: '/api/v1/users'
      },
      {
        method: 'POST', 
        path: '/api/v1/login',
        body: { token: 'nrg55xwrd45' }
      }
    ]
}
```
