feat: Add Drupal testing workflow and Docker build trigger

feat: Add Drupal testing workflow and Docker build trigger This commit introduces a new GitHub Actions workflow (`test-drupal.yml`) designed to test Drupal installations. It also modifies the existing `docker-buildx.yml` workflow to be triggered by the successful completion of the Drupal testing workflow when the target branch is `main`. Key changes include: - **New `test-drupal.yml` workflow:** - Sets up basic Drupal project structure and installs Drupal using Drush. - Utilizes Docker Compose to spin up Nginx and PHP-FPM/Apache services. - Runs validation scripts to ensure Drupal is installed and functional. - Captures logs and uploads test artifacts for analysis. - **Modified `docker-buildx.yml` workflow:** - Now includes a `workflow_run` trigger that activates after the "Test Drupal Installation" workflow completes successfully on the `main` branch. - The `push` and `pull_request` triggers on `main` are still present for direct pushes. - Conditionals are updated to ensure Docker images are only pushed to Docker Hub for successful runs on the `main` branch. - **New Docker Compose files and scripts:** - `tests/docker-compose.yml` and `tests/docker-compose.fpm.yml` for defining test environments. - `tests/install-drupal.sh` for automating Drupal installation. - `tests/verify-drupal.sh` for performing post-installation verification. - `tests/nginx.conf` for Nginx configuration within the test environment.