[6.x] Allow extending asset preset generation command (#14521)

Author: daun

src/Console/Commands/AssetsGeneratePresets.php

@@ -78,7 +78,7 @@ public function handle()
      * @param  \Statamic\Contracts\Assets\AssetContainer  $container
      * @return void
      */
-    private function generatePresets($container)
+    protected function generatePresets($container)
     {
         $assets = $container->assets()->filter->isImage();
         $counts = [];