feat(lib): add function the concatenates paths with a prefix to a list

lib/default.nix

@@ -19,6 +19,13 @@
                 && (lib.strings.hasSuffix ".nix" path) # include .nix files
               )
           )
-          (builtins.readDir path)));
+          (builtins.readDir path)
+        )
+      );
+  concatPathsWithPrefix = { prefix, path }:
+    builtins.concatLists 
+      [
+        (builtins.map (path: "${prefix}/${path}") paths)
+      ];
 }