ddns-scripts: add support for tb.netassist.ua

[korolartemnexus]

Please add NetAssist :: IPv6 Tunnel Broker
correct custom update url is https://tb.netassist.ua/autochangeip.php?l=[USERNAME]&p=[PASSWORD]&ip=[IP]

If you have the dynamic IP, you can use the auto-update endpoint URL: http(s)://tb.netassist.ua/autochangeip.php?l=YOURLOGIN&p=YOURPASSWORD&ip=YOURIP
The update time is less than 60 seconds.

[kbabioch]

I've proposed a pull request to address this: #27960