cube: add coaching.lakhwara.com nginx conf

hosts/cube/default.nix

···
 
   services.nginx.enable = true;
   services.nginx.virtualHosts."coaching.lakhwara.com" = {
-    forceSSL = serviceConfig.enableSSL;
-    enableACME = serviceConfig.enableSSL;
+    forceSSL = true;
+    enableACME = true;
     locations."/" = { root = "/var/lib/coaching"; index = "/index.html"; };
   };
 }