Add debug trace

[nenad]

What does this PR do?

Adds DebugTrace feature which returns X-Debug-Trace response header with the Trace ID.

Edit: I've reworked the PR so that now we match against some arbitrary key, instead of relying on true or 1 set on the request header.

[codecov[bot]]

Codecov Report

Merging #407 into master will increase coverage by 0.21%. The diff coverage is 84.61%.

@@            Coverage Diff             @@
##           master     #407      +/-   ##
==========================================
+ Coverage   40.27%   40.48%   +0.21%     
==========================================
  Files          75       76       +1     
  Lines        2642     2655      +13     
==========================================
+ Hits         1064     1075      +11     
- Misses       1516     1517       +1     
- Partials       62       63       +1

Impacted Files	Coverage Δ
pkg/config/specification.go	61.81% <100%> (+0.7%)	:arrow_up:
pkg/middleware/debug_trace.go	83.33% <83.33%> (ø)

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[nenad]

@vgarvardt and @rafaeljesus I've updated the PR to be more strict on what is considered a valid debug request. I'd appreciate if you could review it once again.

[rafaeljesus]

int-test are failing