Concatenating upstream responses

Hi, I'd like to concatenate some upstream responses when nginx is configured as a reverse proxy server. Something like this:

```
location / {
concat on;
proxy_pass http://upstream:3000/;
}
```

Is this possible?

Start by reviewing the nginx reverse-proxy location shown in the issue and the module's handling of upstream responses. Determine whether concatenating those responses is supported or define the required behavior for the configuration example; the issue provides no file or test entry point, so the relevant implementation and validation locations must first be identified.

Written by the indexing model from the issue text.