Set root folder for appDataFolder spaces

[dragermrb]

This PR allows to use appDataFolder as spaces.

Actually this library uses 'root' as the root folder. The name 'root' is an alias to My Drive, but this alias only works on 'drive' spaces.

If you want to use appDataFolder space it doesn't works because 'root' is not a valid parent root folder.

Taking the Laravel Example, at the ServiceProvider, look at $options:

namespace App\Providers;

use Illuminate\Support\Facades\Storage;
use Illuminate\Support\ServiceProvider;

class AppServiceProvider extends ServiceProvider { // can be a custom ServiceProvider
    // ...
    public function boot(){
        // ...
        try {
            \Storage::extend('google', function($app, $config) {
                $options = [
                    'spaces' => 'appDataFolder', // <==== This will fail without this PR
                ];

                if (!empty($config['teamDriveId'] ?? null)) {
                    $options['teamDriveId'] = $config['teamDriveId'];
                }

                $client = new \Google\Client();
                $client->setClientId($config['clientId']);
                $client->setClientSecret($config['clientSecret']);
                $client->refreshToken($config['refreshToken']);
                
                $service = new \Google\Service\Drive($client);
                $adapter = new \Masbug\Flysystem\GoogleDriveAdapter($service, $config['folder'] ?? '/', $options);
                $driver = new \League\Flysystem\Filesystem($adapter);

                return new \Illuminate\Filesystem\FilesystemAdapter($driver, $adapter);
            });
        } catch(\Exception $e) {
            // your exception handling logic
        }
        // ...
    }
    // ...
}

[masbug]

Thank you!