Authenticated DNS-over-HTTPS Requests/Clients

### 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

When exposing DoT or DoH publicly many people reported just what I experienced myself multiple times - botnet pingings and malicious clients connecting from all over the world. Since standart DNS implementations and clients don't support authentication for the DNS request to succeed I looked for hacky ways to achieve just that.

### Proposed solution

Apparently AdGuard DNS (afaik your paid DNS service) just added this feature 2 days ago!
- https://adguard-dns.io/en/blog/private-adguard-dns-v2-7.html
This way we can easily authenticate users and control who can use our selfhosted instances way better. I believe it would be a gamechanger and many people would be interested in this. It would be great to have authentication for DNS-over-TLS & DNS-over-QUIC and DNSCrypt as well but seeing there is a ready implementation for DoH would make it easier for AdGuardHome to support this.

### Alternatives considered and additional information

Alternative solutions one can use for now:
- Under `Access Settings` > `Allowed Clients` add your local subnet(s) like `192.168.0.1/24` etc.
- If you still want to use DoT/DoH also paste your [ClientID](https://github.com/AdguardTeam/AdGuardHome/wiki/Clients#clientid) in a new line.

This works well, but many use different reverse proxies in front of AdGuardHome, configuring some of them will be hard, especially having to configure level-2 subdomains (ones like `client-name.adguardhome.example.org` - a certificate would be needed for `*.adguardhome.example.org`).