Minor AdGuard fixes

[a1346054]

• made the capitalization of 'AdGuard' consistent
• added actual SNI for the DoH entries instead of the IP address
  • the SNI was obtained from the certificate, giving highest priority to the first entry openssl s_client -connect "$server_ip":443 </dev/null 2>/dev/null | openssl x509 -noout -text | grep -A1 "X509v3 Subject Alternative Name:" | tr ',' '\n' | sed 's/^ *//'
• added IPv6 versions of DoH