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": "b1cbb6e9-36ea-56ce-abd4-07443a6ae69c",
    "type": "shifts",
    "attributes": {
      "schedule_id": "89289339-95fc-4065-9782-04d70075cb78",
      "rotation_id": null,
      "starts_at": "2025-10-30T07:32:51.000-07:00",
      "ends_at": "2025-10-31T05:32:51.000-07:00",
      "is_override": true
    },
    "relationships": {
      "shift_override": {
        "data": {
          "id": "139564cf-1fcb-408d-a475-67a68c0d11bd",
          "type": "shift_overrides"
        }
      },
      "user": {
        "data": {
          "id": "396",
          "type": "users"
        }
      },
      "assignee": {
        "data": {
          "id": "396",
          "type": "users"
        }
      }
    }
  }
}