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": "ce792d92-5f8a-456d-be2b-cdfeb03c8429",
    "type": "shifts",
    "attributes": {
      "schedule_id": "8c12bbe8-1efb-4f87-9a25-8db569af0eca",
      "rotation_id": null,
      "starts_at": "2025-05-29T19:46:52.000-07:00",
      "ends_at": "2025-05-30T17:46:52.000-07:00",
      "is_override": true
    },
    "relationships": {
      "shift_override": {
        "data": {
          "id": "1c455459-e529-48a0-9cf3-441dd69baef4",
          "type": "shift_overrides"
        }
      },
      "user": {
        "data": {
          "id": "336",
          "type": "users"
        }
      }
    }
  }
}