Adds functional tests

Requires https://www.drupal.org/project/dsfr/issues/3450397 🐛 Invalid schema file for Theme Active in order to success.

https://git.drupalcode.org/issue/dsfr-3476955/-/pipelines/293208

Note some CS has already been fixed in https://www.drupal.org/project/dsfr/issues/3393258 📌 Automated Drupal 10 compatibility fixes Needs review , i can finish CS work to validate project for its acceptance as security covered project.