Changed external wiki query method to prevent attribute caching

What does this MR do?

In https://gitlab.com/gitlab-org/gitlab-ce/commit/740f07b1ec16e225a29e4b910e64775dd3985e88 we added a new tab entry in the sidebar if there was an external service configured. We have had issues with one project because of this. According to the db results, has_external_wiki? is returning true while there is no external wiki service attached. This may be caused by attribute caching.

In this MR we change the method used to avoid this caching and this problem.

What are the relevant issue numbers?

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/57228

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated via this MR
• Documentation reviewed by technical writer or follow-up review issue created
• Tests added for this feature/bug
• Tested in all supported browsers
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• Link to e2e tests MR added if this MR has Requires e2e tests label. See the Test Planning Process.
• Security reports checked/validated by reviewer