you can override the Xdebug configuration using Volume Mounts to substitute your own template file. Copy the original template into your project and make the necessary changes.
Commit your version of the file and add a volume mount to your docker-compose manifest with an entry such as:
./env/local/xdebug.ini.tmpl:/etc/confd/templates/xdebug.ini.tmpl
Once that's in place, you will have to restart the container to pick up the new volume mount:
docker-compose restart www