Add response size to LogFormatterParams

[phacops]

Here is a change to make the response body size an available log formatter param.

[codecov]

Codecov Report

Merging #1752 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #1752      +/-   ##
==========================================
+ Coverage   98.48%   98.48%   +<.01%     
==========================================
  Files          41       41              
  Lines        2049     2050       +1     
==========================================
+ Hits         2018     2019       +1     
  Misses         19       19              
  Partials       12       12

Impacted Files	Coverage Δ
logger.go	100% <100%> (ø)	⬆️

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[sairoutine]

It looks good to me.
To add the unit test will make your PR greater.