Add drush commands for getting and putting files

Problem/Motivation

We have use in enabling drush to put and get files stored on remote systems.

Allowing drush to use the same filesystem wrappers as configured with Flysystem and Drupal enables us a) utilise the same configuration as the Drupal installation b) switch the filesystem depending on environment in the same way we we're doing for our Drupal installation.

This might not be a feature that warrants inclusion in the full version of this module, but leaving it here so that we can track our reasoning for using this as a patch at least.