Static DNS HLD (#1262)

The access to the DNS in SONiC is organized via the resolver configuration file (/etc/resolv.conf). resolv.conf is the plain text file that contains the human-readable configuration. It is used across various subsystems in the SONiC to translate domain names into IP addresses. 

With the current implementation dynamic DNS configuration can be received from the DHCP server or static configuration can be set manually by the user. However, SONiC doesn't provide any protection for the static configuration. The configuration that is set by the user can be overwritten with the dynamic configuration at any time.

The proposed solution is to add support for static DNS configuration into Config DB. To be able to choose between dynamic and static DNS configurations `resolvconf` package.