creates an override shift

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

{
  "data": {
    "id": "e5efb717-da43-4fc0-a2d5-807f2614633d",
    "type": "shifts",
    "attributes": {
      "schedule_id": "1442cb1d-ea49-4a7b-9a73-39dab0248e33",
      "rotation_id": null,
      "starts_at": "2025-06-21T14:01:54.000-07:00",
      "ends_at": "2025-06-22T12:01:54.000-07:00",
      "is_override": true
    },
    "relationships": {
      "shift_override": {
        "data": {
          "id": "295e5ddf-e2ba-4103-955c-08bdd2f1fac9",
          "type": "shift_overrides"
        }
      },
      "user": {
        "data": {
          "id": "346",
          "type": "users"
        }
      }
    }
  }
}