Migrate correlation and tracing code to LabKit

What does this MR do?

Migrate correlation and tracing code to LabKit

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.

What are the relevant issue numbers?

Related to https://gitlab.com/gitlab-org/labkit-ruby/merge_requests/1

EE Companion to https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/25379

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated via this MR
• Documentation reviewed by technical writer or follow-up review issue created
• 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.
• EE specific content should be in the top level /ee folder
• For a paid feature, have we considered GitLab.com plans, how it works for groups, and is there a design for promoting it to users who aren't on the correct plan?
• Security reports checked/validated by reviewer