Introduction of TransactionTracer

TransactionTracer is designed to keep track of request metadata and most important metrics that influenced its performance in the most significant way.

@Wikia/platform-team Please review (I recreated the pull request to make a clean start as I added a bunch of changes)

Coming soon (in separate pull requests):
* log key attributes along with profilers data
* log key attributes along with RUM metrics
That pattern plays well here but fails for more complex case like this: https://github.com/Wikia/app/pull/4007/files#diff-f8d94fd56dab7cc45cdf9c79e833dc41R273

Any ideas for a solution that would be nice and work for the latter case too?