os-bind: allow to specify primaryip's port for secondary zone

[loopway]

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Is your feature request related to a problem? Please describe.
It is not possible to specify a non-standard ip port in the opnsense GUI for the primary ip's of a secondary zone.

Describe the solution you'd like
Possibility to specify no-standard ip port in the opnsense GUI for the primary ip's of a secondary zone. My use-case is two opnsense instances with os-bind installed acting as a primary/secondary dns server each with unbound dns query forwarding configured for the zones. unbound listens to port 53, bind listens to port 53530.

Describe alternatives you've considered
None with this use-case, unless secondary or primary is not a opnsense host.

Additional context

Screenshot:

I will provide a pull request.