Nextcloud container name in config file?

[krair]

For the Nextcloud container, we put it in "maintenance mode" before creating the backup to ensure we pause any actions. This is probably not necessary due to the nature of modern databases, but good practice nonetheless. Thus we need to use the name of the Nextcloud App container to run the appropriate occ command.

This should not be hard-coded into the db_backup.sh script and instead put in the docker_databases (or otherwise) file.