Specific error for gateway timeout

[thaugrud]

Is your feature request related to a problem? Please describe
Currently you can't tell the difference between hiscores being unavailable or the request simply timing out. The hiscores are often very slow, but operational. Distinguishing these scenarios is useful for knowing if it is worth increasing timeout limit.

Describe the solution you'd like
A specific error 504 gateway timeout or possibly 408 request timeout to indicate it was a timeout issue rather than unavailable service.

export class GatewayTimeoutError extends HttpError {
  constructor(msg: string) {
    super(msg, 504);
  }
}

Describe alternatives you've considered
Guessing if it was a timeout or unavailable error.