AUTH-API: Modify add affilication user story to not use /tokens endpoint

We have a temporary stop-gap in place to create an entity when a user attempts to affiliate with an entity. We need to remove this, and use a service account to load entities and passcodes.

The POST to /entities should also be modified to update an entity if it already exists. It should also have the required roles set to 'system' as @pksumesh has added this role to the service account being used.