META: Consider the use of config filter to extend the core provided export command

I think this feature request is not really feasible. Config Filter allows other modules to change what is written to and read from the sync storage. Drush imports and exports everything so a separate command for exporting only certain config can make sense.

However, it would be pretty easy to make the commands work with config filter if http://cgit.drupalcode.org/config_partial_export/tree/config_partial_exp... would use the sync storage service if the directory is the CONFIG_SYNC_DIRECTORY.

for example:

if ($label == CONFIG_SYNC_DIRECTORY) {
  $destination_storage = \Drupal::service('config.storage.sync');
  destination_dir = 'default'; // this is just used as a string afterwards...
}
else {
  $destination_dir = config_get_config_directory($label);
  $destination_storage = new FileStorage($destination_dir);
}