Add DNS SDE Extension Option

### 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

It gets old just having a website just show an error with having to go into the AdGuard settings and it would be nice for a Home product to allow the family guests the option to request an allowlist without having to ask what page they need unblocked or just what's going on, on their device. I have had people complain or just simply not want to use my network because it won't allow them through to a certain website that might not need to be blocked.

### Proposed solution

It would be nice to have it redirect to a full fledged webpage where a user on the network could request the website to be unblocked, etc. It would explain to guests exactly what's going on, etc. You could use the DNS SDE and have it redirect to a webpage created with HTML/CSS/JS with the option in settings to allow requests. Additionally, a link to add to allowlist. It could be super simple to setup since the SDE already contains most of the code.

### Alternatives considered and additional information

_No response_