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": "<string>",
    "type": "shifts",
    "attributes": {
      "schedule_id": "<string>",
      "rotation_id": "<string>",
      "starts_at": "<string>",
      "ends_at": "<string>",
      "is_override": true,
      "created_at": "<string>",
      "updated_at": "<string>",
      "shift_override": {
        "data": {
          "id": "<string>",
          "type": "shift_override",
          "attributes": {
            "shift_id": "<string>",
            "created_by_user_id": 123,
            "created_at": "<string>",
            "updated_at": "<string>"
          }
        }
      },
      "user_id": 123,
      "user": {
        "data": {
          "id": "<string>",
          "type": "users",
          "attributes": {
            "email": "<string>",
            "created_at": "<string>",
            "updated_at": "<string>",
            "first_name": "<string>",
            "last_name": "<string>",
            "full_name": "<string>",
            "full_name_with_team": "<string>",
            "time_zone": "<string>"
          },
          "relationships": {
            "role": {
              "data": {
                "id": "<string>",
                "type": "roles"
              }
            },
            "on_call_role": {
              "data": {
                "id": "<string>",
                "type": "on_call_roles"
              }
            }
          }
        }
      }
    }
  }
}