Add example of React SPA app with Python backend

[rosmo]

This blueprint contains a simple React single page application created with create-react-app and necessary Terraform resources to deploy it in on Google Cloud. The blueprint also contains a very simple Python backend that returns Hello World.

This example incorporates several HTTP security features like:

• Hashes script files for Content-Security-Policy
• Cross domain control for backend
• Backend ingress settings
• Minimally permissioned service accounts
• Cloud Armor Policy
• Support for Identity-Aware Proxy