Starting from June 2025, the default version for new Cloud Composer environments changes from Cloud Composer 2 to Cloud Composer 3

## Change Starting from June 2025, the default version for new Cloud Composer environments changes from Cloud Composer 2 to Cloud Composer 3\. New environments will use the latest default Airflow build (`composer-3-airflow-2`). Currently, the default version is `composer-2-airflow-2`.