provide etc/kconfig in updater output

this is for debugging/documentation purposes and isn't copied to the
device

modules/outputs/updater/default.nix

@@ -27,7 +27,8 @@ in
 
   config.system.outputs.updater =
     runCommand "buildUpdater" { } ''
-      mkdir -p $out/bin
+      mkdir -p $out/bin $out/etc
+      cp ${o.kernel.config} $out/etc/kconfig
       substitute ${./update.sh} $out/bin/update.sh \
          --subst-var-by toplevel ${o.systemConfiguration} \
          --subst-var-by min_copy_closure ${min-copy-closure}