[#28991] Resolve "Viewing old wiki page version, "Edit" button exists, brings up latest markup"

What does this MR do?

When viewing an old page version, Edit button should be disabled.

Are there points in the code the reviewer needs to double check?

• As discussed in https://gitlab.com/gitlab-org/gitlab-ce/issues/28991, currently this changes disables the edit button. Do we want the "View Markup" button?
• Acceptance specs to test for the presence of the Edit button

Why was this MR needed?

Fix for https://gitlab.com/gitlab-org/gitlab-ce/issues/28991

Screenshots (if relevant)

(Latest version of the Wiki Page)

(Older version of the Wiki Page has no Edit button)

Does this MR meet the acceptance criteria?

• Changelog entry added
• Documentation created/updated
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

https://gitlab.com/gitlab-org/gitlab-ce/issues/28991

Closes #28991 (closed)