ENG-1323: create onboarding routing POC (#2550)

A basic implementation of the onboarding routing and enforcement. The
only thing I'm missing is a migration for migrating existing users to
`TRUE`. Would that just be the same process a regular migration?

GitOrigin-RevId: 9e4690ed8e0ec329cf4dd469c60cf7eab6872a2b

Author: getinnocuous