Add proxy buffer size config to fix Bad Gateway (#1984)

To prevent `upstream sent too big header while reading response header from upstream` error

Author: SCjona

nginx/nginx.conf

@@ -37,6 +37,9 @@ http {
 	proxy_http_version 1.1;
 	proxy_redirect off;
 	proxy_buffering off;
+	proxy_buffer_size          128k;
+	proxy_buffers              4 256k;
+	proxy_busy_buffers_size    256k;
 	proxy_next_upstream error timeout invalid_header http_502 http_503 non_idempotent;
 	proxy_next_upstream_tries 2;