Add parameters related to DNS

[eugulixes]

Add the following parameters related to DNS:

• ENABLE_GOOGLE_DNS
• ENABLE_BASIC_YANDEX_DNS
• ENABLE_FAMILY_YANDEX_DNS
• ENABLE_CUSTOM_DNS

ENABLE_GOOGLE_DNS will allow using the most common DNS server. If one uses the parameter, than the following two lines are added to /etc/resolv.conf

nameserver 8.8.8.8
nameserver 8.8.4.4

ENABLE_BASIC_YANDEX_DNS will allow using a quick and reliable DNS server provided by Yandex. If one uses the parameter, than the following two lines are added to /etc/resolv.conf

nameserver 77.88.8.8
nameserver 77.88.8.1

ENABLE_FAMILY_YANDEX_DNS will allow using the DNS server provided by Yandex with protection from "adult" content. If one uses the parameter, than the following two lines are added to /etc/resolv.conf

nameserver 77.88.8.7
nameserver 77.88.8.3

ENABLE_CUSTOM_DNS will allow users to add any DNS server to /etc/resolv.conf.