add server apps

modules/apps/server.nix

@@ -0,0 +1,23 @@
+{
+  inputs,
+  outputs,
+  lib,
+  config,
+  pkgs,
+  ...
+}: let
+  inherit (lib) mkEnableOption mkIf mkOption types;
+  cfg = config.horseman.apps.server;
+in {
+  options = {
+    horseman.apps.server = {
+      enable = mkEnableOption "Apps that only need to be installed on servers";
+    };
+  };
+
+  config = mkIf cfg.enable {
+    environment.systemPackages = with pkgs; [
+      certbot
+    ];
+  };
+}