Make list of setup tasks configurable through the Config

[schlessera]

Currently, the list of setup tasks is fetched from the method BrightNucleus\Boilerplate\Scripts\Setup::getSetupTasks(), which just builds an array of fully qualified class names.

It would be preferable to read the list of tasks from the Config file, so that when the package gets extended, one can provide a custom list of setup tasks through a custom config file.