Replace digdelv/ans8 with AsyncDnsServer

Replace digdelv/ans8 with AsyncDnsServer

Previously, the ans8 server had different response modes that applied to
all queries. Replace it with AsyncDnsServer that has serves the different
response modes under different domains without the need to change the
server behaviour at runtime.

Add the new queries that require an ns3 fallback to the ns3/example.db
zone.