log all reasons why a connection is closed

[marten-seemann]

Fixes #2647.

[codecov]

Codecov Report

Merging #2669 into master will increase coverage by 0.03%.
The diff coverage is 93.33%.

@@            Coverage Diff             @@
##           master    #2669      +/-   ##
==========================================
+ Coverage   86.62%   86.65%   +0.03%     
==========================================
  Files         122      123       +1     
  Lines        9749     9778      +29     
==========================================
+ Hits         8445     8473      +28     
  Misses        971      971              
- Partials      333      334       +1     

Impacted Files	Coverage Δ
qlog/event.go	95.98% <ø> (ø)
session.go	77.11% <70.00%> (+0.04%)	⬆️
logging/close_reason.go	100.00% <100.00%> (ø)
qlog/qlog.go	95.35% <100.00%> (-0.02%)	⬇️
qlog/types.go	84.92% <100.00%> (ø)

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