Adds inter-service OpenTracing propagation

What does this MR do?

Extends https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/24186 with interservice propagation, and attempt to slim down https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/21280.

This change allows the GitLab rails and sidekiq components to receive tracing spans from upstream services such as Workhorse and pass these spans on to downstream services including Gitaly and Sidekiq.

This change will also emit traces for incoming and outgoing requests using the propagated trace information. This will allow operators and engineers to view traces across the Workhorse, GitLab Rails, Sidekiq and Gitaly components.

Additional intra-service instrumentation will be added in future changes.

What are the relevant issue numbers?

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• Tests added for this feature/bug
• Tested in all supported browsers
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• Link to e2e tests MR added if this MR has Requires e2e tests label. See the Test Planning Process.
• Security reports checked/validated by reviewer