Order system architecture example

Mermaid: paste order-system.mmd into https://mermaid.live/.
Structurizr: replace the sample workspace at https://playground.structurizr.com/ with order-system.dsl and select Render.
draw.io: open order-system.drawio in https://app.diagrams.net/ or the desktop app.

All three show the Customer outside the Order system boundary and the Web app, Order API and Orders database inside it.
