Allow for large upstream response headers

[mdeuser]

Today, response headers >3KB result in a 502 response. Is issue is a request to bump the nginx configuration to allow for header sizes of up to 8KB.

[mhamann]

Changing buffer sizes should be carefully considered, since it changes how much memory needs to be allocated for every request.

I'm a little wary of bumping this globally, since we'd be effectively doubling the amount of memory used in the current configuration.

On the other hand, perhaps 4k is a bit low for a decent number of production use cases and 8k would be more appropriate.

In any case, the configuration change would look like this:

proxy_buffer_size 8k;