Symfony configuration to standalone configuration file generation

[pounard]

The goal is the following:

• allow people to use this bundle as a dev dependency (no code on production),
• they can then dump the static configuration of their doctrine entities in a generated file,
• then an arbitrary container using db-tools as a PHAR file can be arbitrarily used in CI, or the PHAR file can be pushed on a dedicated box for handling the database operations, anonymization etc... outside of the Symfony app context.