dnsdist: add frontend response statistics #7578
Adds new global "frontend" stats for noerror, nxdomain and servfail answers sent to clients (like in the recursor).
If using cache in dnsdist you otherwise lose visibility of the types of answers sent from there.
Stat names are up for discussion, the term frontend seems to be used elsewhere as well. Perhaps servfail-responses and responses should be renamed to backend-* ?
Regression tests are failing because of the new metrics showing up in the API output:
Let me now if you want some help :-)