creates an shadow configuration

curl --request POST \
  --url https://api.rootly.com/v1/schedules/{schedule_id}/on_call_shadows \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/vnd.api+json' \
  --data '{
  "data": {
    "type": "on_call_shadows",
    "attributes": {
      "shadowable_type": "User",
      "shadowable_id": "<string>",
      "shadow_user_id": 123,
      "starts_at": "2023-11-07T05:31:56Z",
      "ends_at": "2023-11-07T05:31:56Z"
    }
  }
}'

{
  "data": {
    "id": "6c2de0c7-5ffd-496c-92b2-81d390ffc506",
    "type": "on_call_shadows",
    "attributes": {
      "schedule_id": "0dc71e6a-301a-4c00-935c-39cbbb804a5d",
      "shadowable_type": "User",
      "shadowable_id": "342",
      "shadow_user_id": 341,
      "starts_at": "2025-07-14T00:17:55.845-07:00",
      "ends_at": "2025-07-15T00:17:55.845-07:00",
      "created_at": "2025-07-12T00:17:55.975-07:00",
      "updated_at": "2025-07-12T00:17:55.975-07:00"
    }
  }
}