Document apos-attachments disabledFileKey option.

[abea]

https://github.com/apostrophecms/apostrophe-redirects/issues/10#issuecomment-392927735

Quoth Tom:

There is now a practical path to fix this:

1. npm update

'apostrophe-attachments': {
  uploadfs: {
    disabledFileKey: 'very-random-string-please-not-this'
  }
}

3. Deploy as usual. (Please note: I put these steps in this order for reasons)

4. On the server, run this task to complete the transition:

   node app apostrophe-attachments:migrate-to-disabled-file-key

Now files in the trash have their names changed rather than their permissions changed. Recommend verifying an example.

BENEFITS

• You can now sync down without permissions nonsense! Woo
• You can now create a redirect for the old URL of the file, because the file ain't there no more.