[EE] Refactor Hashed Storage for future Rollback functionality

What does this MR do?

This is the EE backport from https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/24402

What are the relevant issue numbers?

• https://gitlab.com/gitlab-org/gitlab-ce/issues/53966
• https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/23955
• https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/24402

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