ddclient: T5791: Fix migration to normalize config name and avoid config

Since service dns dynamic address <address> service <service> ...
changed to service dns dynamic name <service> address <address> ...,
the resulting service and address config flip can result in conflicting
service name.

Additionally, since dynamic DNS service name now have name constraint,
we need to normalize the service name to conform with the constraint.

We now migrate the service name to (service|rfc2136)-<service>-<address>
to avoid the conflict and optionally append an index if there is still a
name conflict after normalization.