Add Cognito SSO to django client

[fyliu]

Overview

The django client app needs to authenticate with Cognito, so that it can work with the PD backend.

Action Items

• Add Cognito SSO to the django project
• Make sure it can authenticate with the VRMS user pool
• Add instructions for configuring the Cognito SSO
• Remove Google authentication

Resources/Instructions

• django-allauth page on cognito configuration
• @fyliu to get user pool configs
• the "add cognito login" commit in the django-party repo might be helpful. It also contains the development user pool configs.