Add the Zellij default configuration

Used `zellij setup --dump-config` to get the configuration and saved it
into its own file.

lib/shared/modules/zellij.nix

@@ -1,10 +1,11 @@
+{ self, ... }:
 {
   programs.zellij = {
     enable = true;
   };
 
-  xdg.configFile."zellij/config.kdl".text = ''
-    simplified_ui true
-    theme "catppuccin-mocha"
-  '';
+  xdg.configFile."zellij" = {
+    source = "${self}/config/zellij";
+    recursive = true;
+  };
 }