MEDIUM: resolvers: rename dns extra counters to resolvers extra counters

MEDIUM: resolvers: rename dns extra counters to resolvers extra counters

This patch renames all dns extra counters and stats functions, types and
enums using the 'resolv' prefix/suffixes.

The dns extra counter domain id used on cli was replaced by "resolvers"
instead of "dns".

The typed extra counter prefix dumping resolvers domain "D." was
also renamed "N." because it points counters on a Nameserver.

This was done to finish the split between "resolver" and "dns" layers
and to avoid further misunderstanding when haproxy will handle dns
load balancing.

This should not be backported.