Wrong HTTP status for timeout?

With a simple Dockerfile that always times out after 1s:

```Dockerfile
FROM public.ecr.aws/lambda/nodejs:12
RUN echo 'exports.handler = (_event, _context, cb) => { setTimeout(() => {}, 100000) }' > index.js
ENV AWS_LAMBDA_FUNCTION_TIMEOUT=1
CMD ["index.handler"]
```

Hitting the endpoint:

```
$ curl -qv http://localhost:8080/2015-03-31/functions/function/invocations -d '{}'
* Trying ::1...
* TCP_NODELAY set
* Connected to localhost (::1) port 8080 (#0)
> POST /2015-03-31/functions/function/invocations HTTP/1.1
> Host: localhost:8080
> User-Agent: curl/7.64.1
> Accept: */*
> Content-Length: 2
> Content-Type: application/x-www-form-urlencoded
>
* upload completely sent off: 2 out of 2 bytes
< HTTP/1.1 200 OK
< Date: Tue, 19 Jan 2021 02:38:17 GMT
< Content-Length: 33
< Content-Type: text/plain; charset=utf-8
<
* Connection #0 to host localhost left intact
Task timed out after 1.00 seconds* Closing connection 0
```

Returns status code 200 and no special response headers.

I didn't find conclusive documentation on what exactly should happen, but the [screenshot](https://theburningmonk.com/wp-content/uploads/2019/05/img_5ce5e801baffb.png) on [this page](https://theburningmonk.com/2019/05/how-to-log-timed-out-lambda-invocations/) seems to suggest that a "real" lambda would return 502.

使用提供的Dockerfile重现超时，并使用curl向文档中说明的调用端点发送POST。将模拟器的200响应和标头与链接文章中描述的真实Lambda行为进行比较，然后确定预期的状态和标头；完成的标准是超时响应与该行为一致。

由索引模型根据 Issue 内容生成。