system: wizard new setting for reply-to behaviour configuration

[fichtner]

Important notices

Before you add a new report, we ask you kindly to acknowledge the following:

• I have read the contributing guide lines at https://github.com/opnsense/core/blob/master/CONTRIBUTING.md
• I am convinced that my issue is new after having checked both open and closed issues at https://github.com/opnsense/core/issues?q=is%3Aissue

Is your feature request related to a problem? Please describe.

Since reply-to (force gateway?) can have unintended side effects with other network equipment offer it in the initial wizard.

Describe the solution you like

Add a sensible default to the wizard: the wizard is likely a single-WAN case, but in any case adding the setting there and explaining it better may reduce the risk from the wrong configuration.

Describe alternatives you considered

N/A

Additional context

N/A