Add informations about tables added in the DB by Doctrine after installation

[ttoine]

After a discussion on Slack it appears that they are tables created by Doctrine during the installation of a PrestaShop shop. But, this is not documented in the devdocs.

I created this issue to track this lack of information.

Edit from @jolelievre
We also should document the different other ways of creating/updating the database table:

• db_structure.sql for fresh install
• upgrade sql scripts
• available placeholders like PREFIX_ that can be used in them

This should be documented for a core developer, and for module developers.