os-ddclient / add option to update other hosts or aliases

[nk404030]

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Is your feature request related to a problem? Please describe.
Updating DNS records for dynamic IPv6 would involve setting up a script on every server / service which can lead to overhead and may not update instantly, unlike monitoring the WAN interface on opnsense for reconnects.

Describe the solution you'd like
I would like to be able to set the Check IP method in dynamic DNS to either an alias, with the option to only update public IPv6 addresses from it.

Another useful addition would be using MAC-Addresses for the IPv6-Interface-Identifier to update a record to a SLAAC Address.
Example:
Check IP Method: IPv6-Interface-Identifier
Host-MAC: 11:22:33:aa:bb:cc
Interface: LAN

In this case, opnsense would update the AAAA record to [LAN-Prefix]:1322:33ff:feaa:bbcc when the LAN prefix changes.

Describe alternatives you've considered
Custom Script.

Additional context
N/A

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[nk404030]

Implemented in #4497