Use modern way of loading the bundle's config by extending AbstractBu…

[michaelKaefer]

…ndle instead of Bundle

See https://symfony.com/doc/current/bundles/configuration.html which states:

There are two different ways of creating friendly configuration for a bundle:

Using the main bundle class: this is recommended for new bundles and for bundles following the recommended directory structure;
Using the Bundle extension class: this was the traditional way of doing it, but nowadays it's only recommended for bundles following the legacy directory structure.

And see https://symfony.com/doc/current/bundles/best_practices.html which states:

This directory structure is used by default when your bundle class extends the recommended AbstractBundle. If your bundle extends the Bundle class, you have to override the getPath() method ...