feat(builder): Allow the user to use a pre-owned version of extracted files (maps / vmaps / etc...)

[Byloth]

In the Wiki we described the process of extracting files from a WoW client as the unique alternative to populate these files when using CMaNGOS Docker.

The process is quite time-consuming and these client files never change...
What if a user already has these files somewhere? Do they need extract them again? Wouldn't it be enough to copy them?

Create a specific command in the the builder/entrypoint.sh shell script to allow users to copy a pre-owned directory with these extracted files directly into the cmangos_mangosd_data volume used by CMaNGOS Docker.