Update schema key to receive a f11s json

[hannelita]

Acceptance

• A request must send a f11s object on the schema field

On the body of the request, send

"schema": {
    "fields": [
          {
            "name": "FID",
            "type": "integer",
            "format": "default"
          },
          {
            "name": "Mkt-RF",
            "type": "number",
            "format": "default"
          }
     ]
  }

Tasks

• Core lib refactor to process the f11s obj instead of an array with the names of the fields
• Update docs
• Fix tests