code: private function addBundles(ContainerBuilder $container): void
      {
          $packages = $container->getDefinition('assets.packages');
          $context = new Reference('contao.assets.assets_context');
  
          if ($container->hasDefinition('assets._version_default')) {
              $version = new Reference('assets._version_default');
          } else {
              $version = new Reference('assets.empty_version_strategy');
          }
  
          $bundles = $container->getParameter('kernel.bundles');
          $meta = $container->getParameter('kernel.bundles_metadata');
  
          foreach ($bundles as $name => $class) {
              if (!is_dir($meta[$name]['path'].'/Resources/public')) {
                  continue;
              }
  
              $packageVersion = $version;
              $packageName = $this->getBundlePackageName($name);
              $serviceId = 'assets._package_'.$packageName;
              $basePath = 'bundles/'.preg_replace('/bundle$/', '', strtolower($name));
  
              if (is_file($meta[$name]['path'].'/Resources/public/manifest.json')) {
                  $def = new ChildDefinition('assets.json_manifest_version_strategy');
                  $def->replaceArgument(0, $meta[$name]['path'].'/Resources/public/manifest.json');
  
                  $container->setDefinition('assets._version_'.$packageName, $def);
                  $packageVersion = new Reference('assets._version_'.$packageName);
              }
  
              $container->setDefinition($serviceId, $this->createPackageDefinition($basePath, $packageVersion, $context));
              $packages->addMethodCall('addPackage', [$packageName, new Reference($serviceId)]);
          }
      }
docs: Adds every bundle with a public folder as assets package.