per-request verbose logging and debug log improvements

This new approach uses per-request variables in Lua and creates new
callback for each DEBUG_IF call instead of each request.

Intended usage: Quick resolution attempt with an empty cache.

export QNAME=...
export QTYPE=...
sudo -E docker run -e QNAME -e QTYPE krestest:latest '-n' '-c' '/etc/knot-resolver/kresd.conf'

It creates new callback functions for every request which
uses "callback chaining" but these should be rare.

It seems there is no reason to keep this function private in policy
module.

It did not log through request->trace_log and is not very useful anyway.

DEBUG_IF accepts user-supplied function which decides which requests
should be logged.

Attempt to avoid duplicating ten lines in debug_logfinish_cb lead me
to splitting kr_log_qverbose_impl into two functions kr_log_q and kr_log_req.
This is another minor change to API exposed to modules.

Formerly both logs used slightly different formats and duplicated code.
From now on verbose log and request tracing are generated using the same
code.

This required a small change to request trace_log_f definition so it
might affect external modules.

We de-randomize qname letter case very early so kr_pkt_text() should see
all lowercase. Any uppercase means mismatch.

I've considered moving debug print to an earlier place but this way it
is more visible so I like more.