Disable query limit counter in sidekiq

What does this MR do?

If Sidekiq::Testing.inline! is used, SQL transactions done inside Sidekiq worker are included in the SQL query limit (in a real deployment sidekiq worker is executed separately). To avoid increasing SQL limit counter, the request is marked as whitelisted during Sidekiq block.

What are the relevant issue numbers?

Related to https://gitlab.com/gitlab-org/gitlab-ee/issues/7087

Related discussion in: https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/6983#note_97094971

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• Tests added for this feature/bug
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides