Enabling DNS Filter Support for Custom Domain Upstream

### Issue Details

dnsproxy, which is now widely available in AdGuard products, supports specifying specific DNS upstream servers for each domain in a configuration file.
- https://github.com/AdguardTeam/dnsproxy#specifying-upstreams-for-domains
- https://github.com/AdguardTeam/AdGuardHome/wiki/Configuration#upstreams-for-domains

But this feature does not work with regular DNS filters, so you must run a DNS proxy server locally to split the traffic to the upstream servers.

### Proposed solution

Make the DNS filter syntax support specifying upstream resolving servers.
> https://adguard-dns.io/kb/general/dns-filtering-syntax/

### Alternative solution

_No response_