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": "03429765-1063-440f-b9b1-431e9c03bc1d",
    "type": "schedule_rotation_users",
    "attributes": {
      "schedule_rotation_id": "5f1543f3-c694-46d8-a934-62b968e57354",
      "user_id": 857,
      "position": 2,
      "created_at": "2026-01-23T02:22:52.209-08:00",
      "updated_at": "2026-01-23T02:22:52.209-08:00"
    }
  }
}