Creates a schedule rotation user

curl --request POST \
  --url https://api.rootly.com/v1/schedule_rotations/{schedule_rotation_id}/schedule_rotation_users \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/vnd.api+json' \
  --data '{
  "data": {
    "type": "schedule_rotation_users",
    "attributes": {
      "user_id": 123,
      "position": 123
    }
  }
}'

{
  "data": {
    "id": "edaa0fd0-1f43-41c4-a1c5-a5229efab1a9",
    "type": "schedule_rotation_users",
    "attributes": {
      "schedule_rotation_id": "e966bcdc-4420-4e34-aabe-c9eee636a35b",
      "user_id": 439,
      "position": 2,
      "created_at": "2025-03-26T23:24:39.528-07:00",
      "updated_at": "2025-03-26T23:24:39.528-07:00"
    }
  }
}