FE Import history - Add group import history menu items

What does this MR do and why?

This creates a blank Group Import History page. Users with owner or admin privileges in the near future can access this consolidated history of imports for each group.

This MR is the start of that epic:

• adds an import history page for the group that is only accessible to group owners or higher, at /groups/<GROUPNAME>/-/import_history
• introduces the feature flag :group_import_history_visibility

As the backend work for the group-level import history data is still ongoing, the page is blank for now. Adding the page to the super sidebar menu also depends on backend. For now the page is not linked anywhere.

References

Epic - &17359

Screenshots or screen recordings

Before	After
Group - owner	Group - owner
Group - non-owner, just member	Group - non-owner, just member

How to set up and validate locally

1. In rails console enable the feature flag

   Feature.enable(:group_import_history_visibility)

2. Find a group for which your user is an owner.

3. Navigate to groups/<your-group>/-/import_history to view the empty import history page

4. Navigate to admin/groups/<your-group> and note the name of a group member who is not an owner

5. Navigate to admin/users, search for your chosen member and click on the member

6. Click Impersonate in the top right of the user page

7. Navigate to the import history page for the group and you should receive a 404

8. To stop impersonation, on the homepage sidebar, top left, click the sketchy-looking black icon next to your user avatar

   

MR acceptance checklist

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Related to #534493 (closed)