nixos/headscale: fix derp.auto_update_enabled option

The options part of "services.headscale.settings" get rendered directly
into a JSON file. As such, any declared values need to match the actual
config key that upstream uses or they are ineffective.

One such key is "derp.auto_update_enable", which controls whether or not
auto-updates for the DERP map are enabled. This key is misspellt though:
the config is called "derp.auto_update_enabled", and that has always
been the case since the config has been introduced in 57f46ded (Split
derp into its own config struct, 2021-10-22). Any unknown key is simply
ignored by Headscale, and as such the setting is ineffective.

Fix this by renaming the option.

Author: pks-t

nixos/modules/services/networking/headscale.nix

@@ -164,7 +164,7 @@ in
                 '';
               };
 
-              auto_update_enable = lib.mkOption {
+              auto_update_enabled = lib.mkOption {
                 type = lib.types.bool;
                 default = true;
                 description = ''
@@ -493,7 +493,11 @@ in
   imports = with lib; [
     (mkRenamedOptionModule
       [ "services" "headscale" "derp" "autoUpdate" ]
-      [ "services" "headscale" "settings" "derp" "auto_update_enable" ]
+      [ "services" "headscale" "settings" "derp" "auto_update_enabled" ]
+    )
+    (mkRenamedOptionModule
+      [ "services" "headscale" "derp" "auto_update_enable" ]
+      [ "services" "headscale" "settings" "derp" "auto_update_enabled" ]
     )
     (mkRenamedOptionModule
       [ "services" "headscale" "derp" "paths" ]