net/wireguard - offer CARP vhid tracking support

[AdSchellevis]

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Is your feature request related to a problem? Please describe.
When Wireguard is initiating a connection and the node is in backup mode, it would be practical to either remove the wg interface or force it down.

Describe the solution you'd like
A similar construction as recently added for OpenVPN Instances (opnsense/core#6836), which should track the relevant vhid as specified on the instance.

Describe alternatives you've considered
none

Additional context