create new report spec needs fixes

[wholmgren]

"normalization" is a valid key for elements of "object_pairs", right? It's included in core's reports tests here and here

{
  "report_parameters": {
    "categories": [
      "total"
    ],
    "costs": null,
    "end": "2019-08-24T14:15:22Z",
    "filters": null,
    "forecast_fill_method": null,
    "metrics": [
      "mae"
    ],
    "name": "string",
    "object_pairs": [
      {
        "aggregate": "0f59de55-2f0e-436a-8ea9-fb197b396fd3",
        "cost": null,
        "forecast": "c1058bd0-c3da-4141-92c6-496be27f264d",
        "forecast_type": "forecast",
        "observation": "5bf24aaf-36fe-45d8-956d-da6551803aa4",
        "reference_forecast": null,
        "uncertainty": null
      }
    ],
    "start": "2019-08-24T14:15:22Z"
  }
}

[wholmgren]

longer list of potential issues with the create new report example json and/or docstring:

• no normalization spec/docs
• filter spec example would be helpful
• cost spec example would be helpful
• forecast fill method not fully documented
• should add nmae and skill to example metrics, reference forecast uuid
• includes both an aggregate and an observation uuid, and docs don't address this