Hello World example app.

This is an extremely simple web application to use as an example in the Cloud Platform User Guide.

The idea is to keep the application as simple as it can possibly be, so that the only thing the user needs to care about is the actual deployment process.

Ideally, this application should stay 'pinned' to the user guide topic. More complex examples, e.g. including RDS or other resources, should use separate example applications, rather than adding any complexity or additional configuration to this application.