[EE] Reduce diff with CE in `spec/policies`

CE back port can be found at https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/26593.

Related to https://gitlab.com/gitlab-org/gitlab-ee/issues/9506.

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
• EE specific content should be in the top level /ee folder
• Security reports checked/validated by reviewer