Create EDA helper module

[benjymoses]

Create a Python helper, and usage instructions, to abstract the creation of conformant event-driven architecture events.

The helper will

• enable users to create and build up a Retail Demo Store event object
• augment events with standardised metadata such as trace IDs and idempotency keys
• discover the correct EventBridge event bus to send messages to

[benjymoses]

Moved back to backlog due to lack of time. Plan to pick up in next sprint.