Feature: #756 - Add Site Set Configuration Loader 

See Issue 756

Description 

If you want to switch to the Site Sets configuration loader, you have to alias the new classes.

You can decide to move some configuration to Site Sets and leave others in TypoScript

$services
    ->alias(
        \Extcode\Cart\Configuration\Loader\PaymentMethodsLoaderInterface::class,
        \Extcode\Cart\Configuration\Loader\SiteSets\PaymentMethodsLoader::class
    )
;
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services:
    Extcode\Cart\Configuration\Loader\PaymentMethodsLoaderInterface:
         alias: Extcode\Cart\Configuration\Loader\SiteSets\PaymentMethodsLoader
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Impact 

No direct impact.