Support multi-upstream DNS servers and optimistic DNS.

@IvanIin

It seems that next AG for iOS will provide the feature of DNS changer, right?

1. Please support DoH, DoT and DNSCrypt v2.

2. Multi-upstream DNS servers such as what is in AG Home.
Examples:
1.1.1.1 - regular DNS (over UDP)
tls://1dot1dot1dot1.cloudflare-dns.com - encrypted DNS-over-TLS
https://cloudflare-dns.com/dns-query - encrypted DNS-over-HTTPS
tcp://1.1.1.1 - regular DNS (over TCP)
sdns://... - you can use DNS Stamps for DNSCrypt or DNS-over-HTTPS resolvers

3. Optimistic DNS project lets all upstream DNS servers resolve domains at the same time and gets the fastest response time.

Surge app supports Optimistic DNS.
https://itunes.apple.com/us/app/surge-3/id1442620678

https://forums.developer.apple.com/thread/110429