In v2.5 we've parametrized DATABASE_DRIVER to be able to configure PostgreSQL support. However when migrating to Symfony 4 via EZP-30387, this parameter disappeared.

Right now we should parametrize also mysql part of DATABASE_URL. In the future we might drop these parameters in favor of user-defined DATABASE_URL.

DATABASE_DRIVER is probably not the best name here and it's not the same as it was in v2.5, so we should choose something different.