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": "74fd48ee-a54f-4d0e-adc3-decf8e9d50ed",
    "type": "shifts",
    "attributes": {
      "schedule_id": "0a6be2f4-bf61-4eba-abe8-0424e07f1b53",
      "rotation_id": null,
      "user_id": 749,
      "starts_at": "2026-01-24T00:59:24.000-08:00",
      "ends_at": "2026-01-24T22:59:24.000-08:00",
      "is_override": true
    },
    "relationships": {
      "shift_override": {
        "data": {
          "id": "7436d6af-1e2b-4ce2-a3f8-d159f0e269a9",
          "type": "shift_overrides"
        }
      },
      "user": {
        "data": {
          "id": "749",
          "type": "users"
        }
      },
      "assignee": {
        "data": {
          "id": "749",
          "type": "users"
        }
      }
    }
  }
}