Stabilize AWS Amplify module

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### Overview:

The AWS Amplify Console provides a Git-based workflow for deploying and hosting fullstack serverless web applications. A fullstack serverless app consists of a backend built with cloud resources such as GraphQL or REST APIs, file and data storage, and a frontend built with single page application frameworks such as React, Angular, Vue, or Gatsby.

[AWS Docs](https://docs.aws.amazon.com/amplify/latest/userguide/welcome.html)

### Maturity: Developer Preview

See the [AWS Construct Library Module Lifecycle doc](https://github.com/aws/aws-cdk-rfcs/blob/master/text/0107-construct-library-module-lifecycle.md) for more information about maturity levels.

### Implementation:

See the [CDK API Reference](https://docs.aws.amazon.com/cdk/api/latest/docs/aws-amplify-readme.html) for more implementation details.

### Issue list:

Start with the linked AWS Docs and CDK API Reference to understand the Amplify service and current module. The issue names no source files or tests; clarify the high-level constructs, use cases, and issue list before work can be considered done.

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