dnsdist: LogResponseAction

[phonedph1]

Short description

dnsdist currently lacks a LogResponseAction but does have other response logging. It would be nice to have some basic LogResponseAction so things can be logged based on RCode, etc.

This version does not do the binary log, but if there is a desire to have LogAction + LogResponseAction the same interface I'll try to do that.

Largely copy&paste from LogAction but added RCode in the log.

> addResponseAction(AllRule(),LogResponseAction("", true, false, true, true))
> Got query for google.ca|A from 127.0.0.1:60897, relayed to 8.8.8.8:53
[1576861363.424282583] Answer to 127.0.0.1:60897 for google.ca. A (No Error) with id 1139
Got answer from 8.8.8.8:53, relayed to 127.0.0.1:60897, took 16722.2 usec

Checklist

I have:

• read the CONTRIBUTING.md document
• compiled this code
• tested this code
• included documentation (including possible behaviour changes)
• documented the code
• added or modified regression test(s)
• added or modified unit test(s)

[rgacogne]

Looks very good, thanks! A bit of documentation in pdns/dnsdistdist/docs/rules-actions.rst would be even better ;-)

[rgacogne]

Looks good, thanks!