be able to install packages at installation

templates/preseed.cfg.j2

@@ -329,7 +329,7 @@ d-i partman/confirm_nooverwrite boolean true
 tasksel tasksel/first multiselect standard
 
 # Individual additional packages to install
-d-i pkgsel/include string openssh-server build-essential
+d-i pkgsel/include string openssh-server build-essential {{ debianunattended_additional_packages | default('') }}
 # Whether to upgrade packages after debootstrap.
 # Allowed values: none, safe-upgrade, full-upgrade
 #d-i pkgsel/upgrade select none