Disabling Plain DNS if DNS-over-Plain-HTTP is used or no DNS used at all

### 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

We can not disable plain DNS if we use DoH via unenctypted DoH behind reverse proxy.

### Proposed solution

Add ability to disable plain DNS if we use DoH behind proxy like Cloudflare, NGINX etc.

### Alternatives considered and additional information

_No response_