Add a complex use case to the /use_cases collection

I would like to add a use case to the existing collection in the /use_cases section of the library. This use case would feature a more complex architecture that leverages a mix of AWS Solutions Constructs and AWS CDK constructs. It would also align with a real-world business problem. For this, I propose adding a use case that deploys a demo business system that has multiple user roles and multiple functions for each role.

### Use Case

I believe this feature would add value to those who are either getting started with the AWS Solutions Constructs library, or who have some experience but would like to see a real-world architecture created using it. This use case would provide valuable code snippets, design patterns, and other elements useful for developers to craft scalable, performant architectures using AWS Solutions Constructs and the AWS CDK.

### Proposed Solution

- Pull request: https://github.com/awslabs/aws-solutions-constructs/pull/179
- Architecture diagram being added shortly to PR for reference

### Other

https://github.com/awslabs/aws-solutions-constructs/pull/179

* [ x ] :wave: I may be able to implement this feature request
* [ ] :warning: This feature might incur a breaking change

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This is a :rocket: Feature Request

Start by reviewing the existing /use_cases collection and the proposed implementation in pull request #179. Use the PR and its planned architecture diagram to understand the intended complex AWS Solutions Constructs and AWS CDK example. Done means the real-world, multi-role business system is added to the collection with the referenced architecture documentation.

Written by the indexing model from the issue text.