The ddclient daemon requires that the configuration file is only
accessible by the ddclient user. This since it typically contains login
information.
(cherry picked from commit 9f4775dbb5)
This avoids the following warning:
Apr 19 10:53:48 xen systemd[1]: [/nix/store/...-unit-ddclient.service/ddclient.service:19] Unknown lvalue 'type' in section 'Service'
As `Type=simple` is the default in systemd, the assignment to the
service type can be simply dropped.
* rewrite to systemd.services
* disable forking to give systemd better control
* verifiably run as ddclient user
* expose ssl option
* unset default value for dyndns server
* rename option "web" to "use" to be consistent with ddclient docs
* add descriptions
* add types to options
* clean up formatting
