Get filter fields for trace search queries.

Example response

{
  "fields": [
    {
      "field": "operation",
      "fieldType": "SpanEventAttribute",
      "description": "A piece of the workflow represented by a span",
      "type": "StringTracingValue",
      "noValuesReason": {
        "code": "HighCardinalityField",
        "message": "Autocomplete has been disabled for this field due to high cardinality."
      }
    }
  ]
}