We re-introduce the dependency of the nginx container on the lms/cms
images. This dependency was removed to address a debugging scenario
which is actually not practical. Without this dependency, we are forced
to use an external docker-specific resolver which makes the local nginx
configuration incompatible with the kubernetes configuration.
Portainer is no longer a global activation flag, because it does not
make much sense in the context of kubernetes. Instead, we use a simpler
"make" command.
Creating soft links to files that do not exist is just madness, let's
stop it. Instead, we take advantage of the CONFIG_ROOT environment
variable, which allows to place lms/cms.env/auth.json files anywhere.
By switching from ubuntu:18.04 to alpine, we reduce the local image size
from 510 to 87 Mb. Because we don't use bash anymore, it's difficult to
rely on chroot, so we just get rid of docker-entrypoint.sh
