Refactor Sidekiq workers to reduce differences between CE and EE

What does this MR do?

This refactors various Sidekiq workers and backports some changes from EE, reducing the amount of differences between CE and EE.

EE version: https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/9215

What are the relevant issue numbers?

https://gitlab.com/gitlab-org/gitlab-ee/issues/8603

Does this MR meet the acceptance criteria?

• 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
• 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