[DEPRECATED] Retrieves a Custom Field

curl --request GET \
  --url https://api.rootly.com/v1/custom_fields/{id} \
  --header 'Authorization: Bearer <token>'

{
  "data": {
    "id": "128",
    "type": "custom_fields",
    "attributes": {
      "slug": "eligendi-expedita-voluptatem-qui",
      "description": "Eum voluptate ratione quia.",
      "enabled": true,
      "position": 1,
      "updated_at": "2025-07-31T05:01:31.241-07:00",
      "created_at": "2025-07-31T05:01:31.241-07:00",
      "kind": "text",
      "label": "Eligendi expedita voluptatem qui.",
      "shown": [
        "incident_form",
        "incident_slack_form"
      ],
      "required": []
    },
    "relationships": {
      "options": {
        "data": [
          {
            "id": "4",
            "type": "custom_field_options"
          },
          {
            "id": "5",
            "type": "custom_field_options"
          }
        ]
      }
    }
  }
}