* Update main.yml
set container customizations to enabled if nextcloud_container_image_smb_enabled is set (OR imagemagick)
* nextcloud_container_image_customizations_smb_enabled activates customizations
* add smbclient installation to docker image, if enabled
see https://github.com/nextcloud/docker/blob/master/.examples/dockerfiles/smb/apache/Dockerfile for source
* Set variable default and revise multiline syntax
Integrate suggestions from @spantaleev
* Refactor code to make only a single, one-line package install
Per suggestion @spanteleev; so that extra files can be deleted without leaving a footprint in the stack of images
