lib: add evalModulesConfig

lib/default.nix

@@ -2,6 +2,12 @@ let
   nixpkgs-lib = import <nixpkgs/lib>;
   lib = with lib; nixpkgs-lib // builtins // {
 
+    evalModulesConfig = modules: let
+      eval = evalModules {
+        inherit modules;
+      };
+    in filterAttrsRecursive (name: _: !hasPrefix "_" name) eval.config;
+
     evalSource = import ./eval-source.nix;
 
     git = import ./git.nix { inherit lib; };