home-manager/state: add packages suboption

modules/home-manager/_private/state/default.nix

@@ -4,6 +4,7 @@
   imports = [
     ./ports.nix
     ./paths.nix
+    ./packages.nix
   ];
 
   options.state = lib.mkOption {

modules/home-manager/_private/state/packages.nix

@@ -0,0 +1,29 @@
+{ lib, ... }:
+
+{
+  options.state =
+    let
+      packagesSubmodule = { lib, ... }: {
+        options = {
+          packages = lib.mkOption {
+            type = with lib.types; attrsOf package;
+            default = { };
+            description = ''
+              Source of truth containing a set of packages. Useful for options
+              where there are no specific options for a package or as a unified
+              source of truth for different module options requiring a package.
+            '';
+            example = lib.literalExpression ''
+              {
+                diff = pkgs.vimdiff;
+                pager = pkgs.bat;
+                editor = pkgs.neovim;
+              }
+            '';
+          };
+        };
+      };
+  in lib.mkOption {
+    type = lib.types.submodule packagesSubmodule;
+  };
+}