website/docs: add port_in_redirect in nginx config to prevent invalid port in redirect (#3397)

* Proposal and fix for issue #3359

By adding `port_in_redirect off` in the configuration for the NginxProxyManager (NPM), will avoid a redirect to port 4443.
Credit to @adtwomey for the suggestions.

https://github.com/goauthentik/authentik/issues/3359

Signed-off-by: Zolo <39656359+zolodev@users.noreply.github.com>

* Adding a comment

Signed-off-by: Zolo <39656359+zolodev@users.noreply.github.com>

Signed-off-by: Zolo <39656359+zolodev@users.noreply.github.com>

website/docs/providers/proxy/_nginx_proxy_manager.md

@@ -7,6 +7,9 @@ For Nginx Proxy Manager you can use this snippet
 proxy_buffers 8 16k;
 proxy_buffer_size 32k;
 
+# Make sure not to redirect traffic to a port 4443
+port_in_redirect off;
+
 location / {
     # Put your proxy_pass to your application here
     proxy_pass          $forward_scheme://$server:$port;