docs: add proxy_http_version 1.1

add proxy_http_version 1.1 as it is required for KeepAlive connections

docs/source/reference/config-proxy.md

@@ -83,6 +83,7 @@ server {
         proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
 
         # websocket headers
+        proxy_http_version 1.1;
         proxy_set_header Upgrade $http_upgrade;
         proxy_set_header Connection $connection_upgrade;
     }