Support for Cloudflare Tunnel

### 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 want to set up an instance of AdGuard Home on my local network with Cloudflare Tunnel allowing access to it from the global Internet for my device when I'm out of my home. However, AdGuard Home doesn't support the use of Cloudflare's Cf-Connecting-IP HTTP Header, so it makes it difficult to track which device is actually doing the DNS requests.

### Proposed solution

Add support for Cf-Connecting-IP HTTP header.

### Alternatives considered and additional information

_No response_