Allow dump request/response body to opentracing's tags

[phanletrunghieu]

I added IsBodyDump to TraceConfig. If it equal true, tracing info will have request & response's body like this image.

[codecov]

Codecov Report

Merging #38 into master will increase coverage by 1.68%.
The diff coverage is 80.00%.

@@            Coverage Diff             @@
##           master      #38      +/-   ##
==========================================
+ Coverage   49.41%   51.09%   +1.68%     
==========================================
  Files           4        5       +1     
  Lines         344      364      +20     
==========================================
+ Hits          170      186      +16     
- Misses        164      168       +4     
  Partials       10       10              

Impacted Files	Coverage Δ
jaegertracing/body_dump_response_writer.go	50.00% <50.00%> (ø)
jaegertracing/jaegertracing.go	40.33% <100.00%> (+6.69%)	⬆️

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[lammel]

Looking good. As it is configurable and off by default no body data (like passwords) is leaked unexpectedly.
Thanks for your contribution @phanletrunghieu