Map bookstack www dir to addon_configs share

[rbr101]

Problem/Motivation

I want to restore an existing bookstack config which consists of MariaDB data and uploaded files and images. The DB is the easy part but for the files there is no easy option to move them to the bookstack add-on.

Proposed changes

Please change the docker config to map the www directory to addon_configs so the files can easily be copied.

Actual behavior

For now stick to my existing bookstack instance running on a different docker host.