Add support for Oblivious DoH

See the original feature request here:
https://github.com/AdguardTeam/AdGuardHome/issues/2406

RFC: https://www.rfc-editor.org/rfc/rfc9230.html

The task consists of the following parts:

* [ ] Support ODoH on the client-side. This is the most important one as for both DnsLibs / AdGuard Home it only makes sense to have ODoH on the client-side.
* [ ] Add support for ODoH to [dnsstamps](https://github.com/ameshkov/dnsstamps)
* [ ] Add support for ODoH server-side. Nice-to-have, but we will probably only need it in dnsproxy.

Once the work is finished, we'll need to open a corresponding issue in DnsLibs.