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": "8cf3711b-234b-5121-b591-285b8fd18a9d",
    "type": "shifts",
    "attributes": {
      "schedule_id": "2951aebc-529a-406a-8445-e3b7ea148e27",
      "rotation_id": null,
      "starts_at": "2025-10-09T10:39:09.000-07:00",
      "ends_at": "2025-10-10T08:39:09.000-07:00",
      "is_override": true
    },
    "relationships": {
      "shift_override": {
        "data": {
          "id": "c55adea1-1596-4fc6-8d46-ebf6665ea3f0",
          "type": "shift_overrides"
        }
      },
      "user": {
        "data": {
          "id": "389",
          "type": "users"
        }
      }
    }
  }
}