What does this MR do?
In !51873 (merged) we merged all the necessary logic to import and export group wikis.
In this MR we enable group wikis' import/export functionality by removing the feature flag.
We also add the UI changes to reflect it.
The doc MR is in !53250 (merged)
Does this MR meet the acceptance criteria?
Code review guidelines
Merge request performance guidelines
Separation of EE specific content