[ZD#857615] fix private content alert for HC searches

:bug: 

Changes to the Help Center API now require that we fetch an access_policy for a section to get it's visibility.

@maximeprades @pdeuter 

#### References:

- [[ZD#857615] Answer Suggestion App - Enabling "Exclude Agent Only topics" does not actually exclude them from search results.](https://support.zendesk.com/agent/tickets/857615?zat=true)