this is intended for settings that are expected within this container deployment, but it could differ from what users could experience from a packaged installation
a default from docker-compose
docker-compose specifies a lot of environment variables
my primary intention so far was that they are more visible in the compose file and can/should be settings that admins want to modify (plus if you have something variable this is nice as well)
There are currently multiple ways how "default" values for configuration values are defined:
user_plugin
isdb
(see https://stash.kopano.io/projects/KC/repos/kopanocore/browse/installer/linux/server.cfg#342)