Manually specify an IP for the Setup Guide

### Prerequisites

- [X] I have checked the [Wiki](https://github.com/AdguardTeam/AdGuardHome/wiki) and [Discussions](https://github.com/AdguardTeam/AdGuardHome/discussions) and found no answer

- [X] I have searched other issues and found no duplicates

- [X] I want to request a feature or enhancement and not ask a question

### The problem

I would like to be able to specify a specific IP to be listed on the Setup Guide page. I have a reserved/floating IP with DigitalOcean which points to my AdGuard Home install. This is so that when there's a new major OS released, I can build a new copy of AGH on a different VPS, get it ready to go, then move the reserved IP to the new server and all devices immediately start using that new server. The problem is that the IP isn't listed in `ip a` on the server, so AGH doesn't see it to add it to the Setup Page.

This is similar to Issue #3973, but not the same.

### Proposed solution

Add a text box to Settings to input an IP Address.
That IP Address is shown on the Setup Page.

### Alternatives considered and additional information

_No response_