feat: add toYAML function

modules/arion.nix

@@ -27,6 +27,17 @@ in {
   options.arion = {
     enable = mkEnableOption (lib.mdDoc "My custom arion config layer module");
 
+    # TODO: move this somewhere else
+    toYAML = mkOption {
+      type = types.anything;
+      readOnly = true;
+      default = name: attrs:
+        pkgs.runCommandCC name {} ''
+          echo '${builtins.toJSON attrs}' |
+          ${pkgs.remarshal}/bin/remarshal --if json --of yaml > $out
+        '';
+    };
+
     rwDataDir = mkOption {
       default = "/var/lib/arion";
       type = types.str;