nixos/user-groups: add a toggle for user account creation

Microscopic change that allows users to toggle user accounts, per user, conditionally.

nixos/doc/manual/release-notes/rl-2505.section.md

@@ -462,8 +462,11 @@
 
 - `gerbera` now has wavpack support.
 
+- A toggle has been added under `users.users.<name>.enable` to allow toggling individual users conditionally. If set to false, the user account will not be created.
+
 - `ddclient` was updated from 3.11.2 to 4.0.0 [Release notes](https://github.com/ddclient/ddclient/releases/tag/v4.0.0)
 
+
 <!-- To avoid merge conflicts, consider adding your item at an arbitrary place in the list instead. -->
 
 ```{=include=} sections

nixos/modules/config/users-groups.nix

@@ -124,6 +124,16 @@ let
 
     options = {
 
+      enable = mkOption {
+        type = types.bool;
+        default = true;
+        example = false;
+        description = ''
+          If set to false, the user account will not be created. This is useful for when you wish to conditionally
+          disable user accounts.
+        '';
+      };
+
       name = mkOption {
         type = types.passwdEntry types.str;
         apply = x: assert (stringLength x < 32 || abort "Username '${x}' is longer than 31 characters which is not allowed!"); x;
@@ -557,7 +567,7 @@ let
           autoSubUidGidRange subUidRanges subGidRanges
           initialPassword initialHashedPassword expires;
         shell = utils.toShellPath u.shell;
-      }) cfg.users;
+      }) (filterAttrs (_: u: u.enable) cfg.users);
     groups = attrValues cfg.groups;
   });