[dnsdist] Enhance domain spoofing

[janeczku]

This is request for enhancing domain spoofing:

1. SpoofAction should accept a FQDN alternatively to an IPv4 in which case the response would return a CNAME record.
2. Allow Lua actions to spoof queries programmatically. Currently we can send queries to pools from within a Lua action (return DNSAction.Pool, "abuse"). The same should be possible for the SpoofAction:

function luarule(remote, qname, qtype, dh, len)
        if(qtype==35) -- NAPTR
        then
                return DNSAction.Spoof, "192.168.0.1" -- spoof domain
        else
                return DNSAction.None, ""
        end
end

[janeczku]

@rgacogne good job! 🎉😄