dns/ddclient: empty ip send to dns provider & replace dyndns by dynu

[Meliox]

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Describe the bug
The current service to lookup external ip ( https://github.com/opnsense/plugins/blob/master/dns/ddclient/src/opnsense/scripts/ddclient/lib/address.py#L35) for dyndns times out (and has been doing so for ages):

curl https://checkip.dyndns.com/
curl: (28) Failed to connect to checkip.dyndns.com port 443 after 300103 ms: Timeout was reached

Subsequently no IP is displayed in GUI and no IP is send to the DNS provider.

The PR resolves two issues following this.

1. Handle bug with empty IP string is send to DNS provider

The lookup returns no parse ip and extract_address returns and empty string. excute only checks for None, hence an empty string was passed to dns provider.

Following the change, a proper error message is displayed in the log files and more importantly it stops the dns update.

Account xxxxx [dynu - ] no global IP address detected, check config if warning persists
Account xxxxx [dynu - ] not modified

2. Remove the deprentied service dyndns and add dynu ipv4 and ipv6. This will "break" lookup for some, and they will need to revist their dDNS config.

To Reproduce
Steps to reproduce the behavior:

1. Go to Dynamic DNS
2. Configure DDNS and use dynu as "Check ip method"
3. "See error in logs and gui"

Expected behavior
DDNS lookup and population of IP working in GUI.

Screenshots
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Relevant log files
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Additional context
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Environment
Software version used and hardware type if relevant.
e.g.:
OPNsense 24.7.11_2-amd64
Plugin: os-ddclient (installed) 1.26