perf: ⚡️ pass in the ability to configure proxy-buffering

[jaskaransarkaria]

When proxy buffering is disabled, NGINX buffers only the first part of a server’s response before starting to send it to the client, in a buffer that by default is one memory page in size (4 KB or 8 KB depending on the operating system). This is usually just enough space for the response header. NGINX then sends the response to the client synchronously as it receives it, forcing the server to sit idle as it waits until NGINX can accept the next response segment. 

proxy-buffering is off by default

https://github.com/kubernetes/ingress-nginx/blob/main/docs/user-guide/nginx-configuration/configmap.md#configuration-options

https://www.nginx.com/blog/avoiding-top-10-nginx-configuration-mistakes/#proxy_buffering-off