code: private static function getDestinationDir(Composer $composer)
      {
          $extras = $composer->getPackage()->getExtra();
          
          return (array_key_exists('app-migrations-dir',$extras)) ?
              $extras['app-migrations-dir'] :
              getcwd().'/app/DoctrineMigrations';
      }
docs: Get the app migrations dir defined in root package, or
  'app/DoctrineMigrations' instead.
  
  @param Composer $composer
  @return string