Fixes#17898
Since #17204, the admin API has only been available through the web
application because of the unconditional requirement to provide a valid CSRF
token.
This commit changes it back to `null_session`, which should make it work
both with session-based authentication (provided a CSRF token) and with a
bearer token.
* Add trending links
* Add overriding specific links trendability
* Add link type to preview cards and only trend articles
Change trends review notifications from being sent every 5 minutes to being sent every 2 hours
Change threshold from 5 unique accounts to 15 unique accounts
* Fix tests