[DynDNS] Improve IP change latency

[SeverinAlexB]

With #63, the IP change latency depends on the zone republishing crontab task which is usually 60min. This latency can be optimized by building a specific cli command that republishes the pkarr zone when a ip change is detected.

With the upcoming Mainline v5 external IP feature, I hope we can resolve external IP addresses each minute.