feat: redirect HTTP requests to HTTPS

Replace the 404 response on port 80 with a 301 redirect to the
equivalent HTTPS URL, so users who type http:// are seamlessly
upgraded to a secure connection.

conf.d/10-defaults.conf.template

@@ -9,7 +9,7 @@ server {
     listen [::]:80 default_server;
     server_name _;
 
-    return 404;
+    return 301 https://$host$request_uri;
 }
 
 server {