List deterministic signals available to evaluators

curl --request GET \
  --url https://api-sandbox.featherhq.com/v1/evals/signals \
  --header 'x-api-key: <api-key>'

{
  "signals": [
    {
      "key": "<string>",
      "label": "<string>",
      "unit": "<string>",
      "aggregations": [
        "<string>"
      ],
      "channels": [
        "<string>"
      ],
      "filters": [
        {
          "key": "<string>",
          "required": false,
          "description": ""
        }
      ],
      "description": ""
    }
  ]
}