Add flysystem with NetStorage adaptor

[janette]

User Story

I want an upload option on my dataset form that sends the file to Akamai NetStorage

https://github.com/akamai/NetStorageKit-PHP https://www.drupal.org/project/flysystem https://flysystem.thephpleague.com/v2/docs/adapter/sftp/

Acceptance Criteria

[janette]

OR Keep the file management outside the dataset creation process, only use the URL field on the metadata form. Similar to the Viewer module, you create the distribution separately first, then move on to the metadata portion.

[grugnog]

Would suggest comparing flysystem with the native PHP filesystem stream wrappers (which is what S3 and various other modules provide)