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": "d2e19197-db08-5e81-bb9d-d60e67118328",
    "type": "shifts",
    "attributes": {
      "schedule_id": "48e36619-5b32-41a8-ae5f-e421a34b8e32",
      "rotation_id": null,
      "starts_at": "2025-11-21T03:21:50.000-08:00",
      "ends_at": "2025-11-22T01:21:50.000-08:00",
      "is_override": true
    },
    "relationships": {
      "shift_override": {
        "data": {
          "id": "0ebe66bb-ff98-4deb-8b39-03403e51b77e",
          "type": "shift_overrides"
        }
      },
      "user": {
        "data": {
          "id": "398",
          "type": "users"
        }
      },
      "assignee": {
        "data": {
          "id": "398",
          "type": "users"
        }
      }
    }
  }
}