Add Google people API to readme

[maximskripnik]

Description

Current documentation does not mention that Google people API has to be enabled for the authentication to work. This makes it really hard to people who are unfamiliar with this to set this type of authentication up correctly.

Steps to reproduce

Try to deploy the system using current README instructions with Google authentication

Actual result

Google authentication does not work

Expected result

Google authentication works

Also let's add an ability to enable error logging for responses from authentication providers. Currently any exception is silently ignored and 403 returned, which makes it a huge struggle to debug this (I had to clone the repo and change the code to understand what is the problem, instead of just using published docker image)