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": "a9d94c50-d3dc-5328-ab9b-92f4ee37ca43",
    "type": "shifts",
    "attributes": {
      "schedule_id": "c0f49bc3-00f1-4bf6-b6bc-059986c6d150",
      "rotation_id": null,
      "user_id": 398,
      "starts_at": "2025-11-28T20:12:17.000-08:00",
      "ends_at": "2025-11-29T18:12:17.000-08:00",
      "is_override": true
    },
    "relationships": {
      "shift_override": {
        "data": {
          "id": "dbccdf81-2874-45d2-be8a-24325ee06598",
          "type": "shift_overrides"
        }
      },
      "user": {
        "data": {
          "id": "398",
          "type": "users"
        }
      },
      "assignee": {
        "data": {
          "id": "398",
          "type": "users"
        }
      }
    }
  }
}