SenderConfiguration

This class holds the configurable addresses for outgoing emails.

Packages can add their own addresses in the package controller on_start method with some code like this:

```$app->extend(
    SenderConfiguration::class,
    static function(SenderConfiguration $configuration): SenderConfiguration {
        return $configuration->addEntry(
            (new SenderConfiguration\Entry(t('Name of the option'), 'email.configuration.key'))
                ->setPackageHandle('your_package_handle')
        );
    }
);
```