Backport various EE changes to Gitlab::Database

What does this MR do?

This backports various changes made to Gitlab::Database in EE. This allows CE code to use these changes, such as the MR https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/20720/. Without this backport we'd be duplicating code for no good reason.

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Tests added for this feature/bug
• Conforms to the code review guidelines
  • Has been reviewed by a Backend maintainer
  • Has been reviewed by a Database specialist
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• If you have multiple commits, please combine them into a few logically organized commits by squashing them
• End-to-end tests pass (package-and-qa manual pipeline job)