Support running under real domain behind Traefik

[anaqreon]

• The /maps/www/config/config.php Nextcloud config file needs to have the domain added to the trusted_domains list.
• Traefik labels need to be added to the /maps/docker-compose.yml file with a placeholder for the real domain name.

Perhaps the domain name should be a new input argument to the init.sh script. It may be better to immediately support a little config file for the init.sh script that allows you to specify domain and Nextcloud admin account username and password, and even the target Maps app git commit.