Set feature flag enabled by default

For the `forward_npm_package_registry_requests` feature flag

ee/app/views/admin/application_settings/_package_registry.haml

-- if Feature.enabled?(:forward_npm_package_registry_requests) && Gitlab.config.packages.enabled
+- if Feature.enabled?(:forward_npm_package_registry_requests, default_enabled: true) && Gitlab.config.packages.enabled
   %section.settings.as-package.no-animate#js-package-settings{ class: ('expanded' if expanded_by_default?) }
     .settings-header
       %h4

ee/changelogs/unreleased/55344-forward-npm-requests-enabled-by-default.yml

+---
+title: Add NPM package requests forwarding to npmjs.org
+merge_request: 26932
+author:
+type: added

ee/lib/api/helpers/packages/dependency_proxy_helpers.rb

@@ -28,7 +28,7 @@ module API
         end
 
         def redirect_registry_request_available?
-          Feature.enabled?(:forward_npm_package_registry_requests) &&
+          Feature.enabled?(:forward_npm_package_registry_requests, default_enabled: true) &&
             ::Gitlab::CurrentSettings.current_application_settings.npm_package_requests_forwarding
         end
       end