targets/darwin: allow configuring application linking (#4809)

Darwin users can disable application linking or change the path where applications are linked.

modules/targets/darwin/linkapps.nix

@@ -1,9 +1,24 @@
 { config, lib, pkgs, ... }:
 
-{
-  config = lib.mkIf pkgs.stdenv.hostPlatform.isDarwin {
+let cfg = config.targets.darwin;
+in {
+  options.targets.darwin.linkApps = {
+    enable =
+      lib.mkEnableOption "linking macOS applications to the user environment"
+      // {
+        default = true;
+      };
+
+    directory = lib.mkOption {
+      type = lib.types.str;
+      default = "Applications/Home Manager Apps";
+      description = "Path to link apps relative to the home directory.";
+    };
+  };
+
+  config = lib.mkIf (pkgs.stdenv.hostPlatform.isDarwin && cfg.linkApps.enable) {
     # Install MacOS applications to the user environment.
-    home.file."Applications/Home Manager Apps".source = let
+    home.file.${cfg.linkApps.directory}.source = let
       apps = pkgs.buildEnv {
         name = "home-manager-applications";
         paths = config.home.packages;