Only do http logging if a debug build is run

[misaochan]

We should not log cookie headers without informing users, due to privacy concerns. For the time being, http header logging should be restricted to debug builds (which will never be released, but can only be built manually via our repo). See https://github.com/commons-app/apps-android-commons/pull/1751/files#r205656568

Tested on Nexus One emulator on API 24, it displays http headers on debug and not on release.

[codecov-io]

Codecov Report

Merging #1795 into 2.8-release will decrease coverage by <.01%.
The diff coverage is 50%.

@@              Coverage Diff               @@
##           2.8-release   #1795      +/-   ##
==============================================
- Coverage         3.65%   3.65%   -0.01%     
==============================================
  Files              186     186              
  Lines             9314    9315       +1     
  Branches           823     824       +1     
==============================================
  Hits               340     340              
  Misses            8951    8951              
- Partials            23      24       +1

Impacted Files	Coverage Δ
...rw/commons/mwapi/ApacheHttpClientMediaWikiApi.java	3.75% <50%> (-0.01%)	⬇️

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