[ZD#731281] fix answer suggestion app showing private alert issue

#bug

Sections that are restricted to logged-in end users will have `visibility: 'restricted'`, so the private content alert will be shown unexpectedly. We need to check for `visibility: 'internal'` instead.

#### References
- [ZD#731281](https://support.zendesk.com/agent/#/tickets/731281)

@maximeprades @vkmita @dbuchi