Allow to import whitelist entries from files

[alexruf]

It would be very helpful to allow users to import whitelist files just like the filter files. This allows users to share and maintain common whitelist entries.
As a previous Pi hole user I am really missing a feature like this in AdGuard Home. There was a community maintained whitelist which contained some hostnames and domains which were safe to unblock or would otherwise break some sites and applications.

It'll be possible when implement #817 #822

[ameshkov]

Closed as dup