Add simple skeleton for sample app

[whummer]

Add simple skeleton for sample app. This is only a very simple first version - to be extended over time..

The app consists of:

• an API Gateway with two endpoints
  • POST /users to create a new user
  • GET /users to retrieve the list of users
• a Lambda function which handles the API requests
• a TypeDB database which contains the user information

The app is defined via Terraform and directly deployed against LocalStack.