feat: Add FrankenPHP variant for Drupal base images

feat: Add FrankenPHP variant for Drupal base images This commit introduces a new FrankenPHP variant (`frankenphp-trixie`) for the Drupal base images. Changes include: - Adding the `frankenphp-trixie` variant to the GitHub Actions workflow for building Docker images. - Updating the README to reflect the new variant and provide an example `docker-compose.yml`. - Modifying the `build.sh` script to include builds for the FrankenPHP variant. - Updating `clean.sh` to remove FrankenPHP related images. - Adding a `Dockerfile` and `Caddyfile` for the FrankenPHP variant.