DEV: Guardian for hiding about stats (PR #9841)

This allows the About site statistics to be hidden for certain users via a plugin.

With the guardian always returning true (core behavior - no change): Screenshot from 2020-05-20 09-26-04


In a plugin I am going to return false for some users, and they will instead see this:

Screenshot from 2020-05-20 09-25-55

GitHub