Add support for enabling and disabling systemd services in the
blueprint. It works like this:
[customizations.services]
enabled = ["sshd", "cockpit.socket", "httpd"]
disabled = ["postfix", "telnetd"]
They are *added* to any existing settings in the kickstart templates.
(cherry picked from commit 1111aee92d)
(cherry picked from commit 69cc1b17f2)