Pattern: Request/Response Aggregator

Deployable demo that shows a customer a couple of implementations of a request/response aggregator
- Show how messages are fanned out and processed in parallel
- Show how to implement in LogicApps
- Show how to implement in Durable Functions
- Discuss When to use what (logicapps vs functions)
- demonstrate message tracking with property promotion, i.e. show all instances where po xyz was processed
- Self-contained demo
- independently deployable
- independent documentation
- Design as a starting point for customers, simple, easy to build upon

Start by defining the self-contained demo structure around the two requested implementations: LogicApps and Durable Functions. Cover parallel fan-out processing, message tracking through property promotion, deployment, and independent documentation; done means customers can deploy and extend the demo and understand when to use each approach.

Written by the indexing model from the issue text.