nginx: set cache control header

deemz.org/configuration.nix

@@ -224,6 +224,7 @@ let secrets = import ../secrets.nix; in
         basicAuth = userlist;
         extraConfig = ''
           autoindex on;
+          add_header Cache-Control max-age=172800
         '';
         proxyWebsockets = true;
       };
@@ -339,4 +340,4 @@ let secrets = import ../secrets.nix; in
   # Before changing this value read the documentation for this option
   # (e.g. man configuration.nix or on https://nixos.org/nixos/options.html).
   system.stateVersion = "21.11"; # Did you read the comment?
-}
+}