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": "342f65ec-67f4-4928-8a1f-03dd5bd7bc7a",
    "type": "schedule_rotation_users",
    "attributes": {
      "schedule_rotation_id": "1156dca6-7d6a-4d0a-aed4-d066b173317a",
      "user_id": 396,
      "position": 2,
      "created_at": "2025-05-29T17:48:02.005-07:00",
      "updated_at": "2025-05-29T17:48:02.005-07:00"
    }
  }
}