Part of a set of changes to add support for dragging and dropping images into the markdown editor.
Adding a view that redirects to a FileAttachment's file. Adding a uuid field to the FileAttachment model, to be used by the view as non-guessable identifier for the FileAttachment.

This view can be accessed at the following url: /users/<username>/file-attachments/<uuid>/

All unit tests pass after making the changes.
Did some manual testing to make sure the view properly redirects to the file, and the file can be viewed.