Fixes #29528, by allowing all users to view history

What does this MR do?

This fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/29528, aligning the permissions for showing a wiki page and viewing its history.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Performance and testing

This exposes the version history of wiki pages. This should be public to all users who can read wiki pages themselves, so it poses no additional risks.