Persistence of config in mosquitto

[pgulb]

User story

As a wis2box admin, I use commands like
mosquitto_passwd -b /mosquitto/config/password.txt username pass
to create users (additional users for GBs to provide clearer logs to see if there are problems with connection for GBs)
and echo -e "\n\nuser username\ntopic read origin/#" >> /mosquitto/config/acl.conf
to create permissions for a user.
The problem is when upgrading to next version, I need to use same commands again to create users, then restart mosquitto.
I think it could be resolved for me and other who issue changes to mosquitto config, by creating a volume at /mosquitto/config directory of mosquitto container.
It would also better reflect containerization idea and let administrator destroy and recreate a container with mosquitto and retain its configuration.

Acceptance criteria

• Mosquitto config persistence after upgrade/removal/recreation of container

Definition of done

• unit/functional tests added/updated
• documentation updated
• live demonstration provided