Add availability to configure show_image_direct_url

This commit:
  - Add the show_image_direct_url parameter (default to false)
  - Fix spelling errors in documentation
  - Fix documentation format (use puppetdoc)
  - Add missing documentation about params

Change-Id: I8e5cb36c19ffa4ae726642a55d8fab5c6cea07b5
Co-Authored-By: Emilien Macchi <emilien.macchi@enovance.com>