[ticket/12620] Allow the user to define multiples environments

https://tracker.phpbb.com/browse/PHPBB3-12620

replace #2521

PHPBB3-12620

I don't think it's possible because to parse the config file we need to build the container and if a class is missing it will fail. Or maybe we could add an other config file (not be integrated to the container) to store the informations related to the environment construction like this one..