Do not inject variable inside the extension Configuration

[DjLeChuck]

Since Symfony 7.4, the file config/reference.php contains configurations of all bundles : https://symfony.com/blog/new-in-symfony-7-4-better-php-configuration

Using a dynamic value for a default value is not a good thing because the value will change at each container compilation, which results in "useless" modification of the file.

web_dir is using the kernel.project_dir which can be used with % placeholder, the value will be replaced during compilation.

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#162