Before this, we were only adding the correlation id to the "acceptable
exceptions" which we handle in code.
But we need to add it to the default raven context so the information
would be available for uncaught exceptions.
This change is a fairly straightforward refactor to extract the tracing
and correlation-id code from the gitlab rails codebase into the new
LabKit-Ruby project.
The corresponding import into LabKit-Ruby was in
https://gitlab.com/gitlab-org/labkit-ruby/merge_requests/1
The code itself remains very similar for now.
Extracting it allows us to reuse it in other projects, such as
Gitaly-Ruby. This will give us the advantages of correlation-ids and
distributed tracing in that project too.
The Correlation ID is taken or generated from received X-Request-ID.
Then it is being passed to all executed services (sidekiq workers
or gitaly calls).
The Correlation ID is logged in all structured logs as `correlation_id`.
This adds a method to track errors that can be recovered from in
sentry.
It is useful when debugging performance issues, or exceptions that are
hard to reproduce.
