Feature request: Please make it possible to enable proxy_buffering

[ghost]

It seems like it might be beneficial to the reliability of an app we run if it was possible to enable the nginx setting proxy_buffering. This seems to be currently hard-coded off, I assume it wouldn't be that much work to make it available via configmap/annotation..

[diazjf]

Since proxy buffering is set at the location level as seen here: https://github.com/kubernetes/ingress-nginx/blob/master/rootfs/etc/nginx/template/nginx.tmpl#L831 then an annotation would be best in this case. It can also be scoped at the http level, then a config-map value is also a good idea.

See http://nginx.org/en/docs/http/ngx_http_proxy_module.html#proxy_buffering