Resolvable placeholders in parameters that can expand

[shule727]

Add support for resolvable parameters.

E.g.

@PurgeOn(Post::class, properties={"updatedAt"}, parameters={"countryAlpha2": "@AppBundle\Service\LocaleResolver"})

namespace AppBundle\Service;

class LocaleResolver
{
    public function resolve(): array
    {
        return [
            'HR',
            'IT',
            ...
        ];
    }
}