Add EE specific feature entries for admin dashboard

What does this MR do?

This MR is EE-specific part of https://gitlab.com/gitlab-org/gitlab-ce/issues/60581

https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/29306 introduced new feature_entry helper for displaying links in admin dashboard.

This MR updates EE-specific elements of admin dashboard to use this helper.

Adding backstage since changelog entry was already added as part of gitlab-ce

Does this MR meet the acceptance criteria?

Conformity

• Code review guidelines

• Merge request performance guidelines

• Style guides

• Separation of EE specific content

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.

• Tested in all supported browsers