nixos/config: add defaultPackages option

readd perl (used in shell scripts), rsync (needed for NixOps) and strace (common debugging tool)

they where previously removed in https://github.com/NixOS/nixpkgs/pull/91213

Co-authored-by: Timo Kaufmann <timokau@zoho.com>
Co-authored-by: 8573 <8573@users.noreply.github.com>

nixos/modules/config/system-path.nix

@@ -41,6 +41,12 @@ let
       pkgs.zstd
     ];
 
+    defaultPackages = map (pkg: setPrio ((pkg.meta.priority or 5) + 3) pkg)
+      [ pkgs.perl
+        pkgs.rsync
+        pkgs.strace
+      ];
+
 in
 
 {
@@ -63,6 +69,21 @@ in
         '';
       };
 
+      defaultPackages = mkOption {
+        type = types.listOf types.package;
+        default = defaultPackages;
+        example = literalExample "[]";
+        description = ''
+          Set of packages users expect from a minimal linux istall.
+          Like systemPackages, they appear in
+          /run/current-system/sw.  These packages are
+          automatically available to all users, and are
+          automatically updated every time you rebuild the system
+          configuration.
+          If you want a more minimal system, set it to an empty list.
+        '';
+      };
+
       pathsToLink = mkOption {
         type = types.listOf types.str;
         # Note: We need `/lib' to be among `pathsToLink' for NSS modules
@@ -102,7 +123,7 @@ in
 
   config = {
 
-    environment.systemPackages = requiredPackages;
+    environment.systemPackages = requiredPackages ++ config.environment.defaultPackages;
 
     environment.pathsToLink =
       [ "/bin"