feat(modulith): implement transactional event publication with postgresql outbox - #376

Overview

Adds a new tutorial submodule modulith-events demonstrating how to implement resilient, asynchronous inter-module domain event publication using Spring Modulith's Event Publication Registry and a PostgreSQL transactional outbox.

Key Changes

• Module Architecture: Structured domain boundaries with @Modulithic for order, inventory, notification, and shared events in common.
• Durable Outbox: Integrated spring-modulith-starter-jdbc and spring-modulith-events-jdbc to persist unpublished/in-flight events to PostgreSQL upon commit.
• Asynchronous Consumption: Implemented @ApplicationModuleListener in downstream consumer modules (inventory, notification).
• Testcontainers Integration:
  • OrderEventPublicationTests: Verified asynchronous completion in the outbox using PostgreSQL Testcontainers with @ServiceConnection and Awaitility.
  • ModulithEventsApplicationTests: Enforced encapsulation and architectural compliance using ApplicationModules.verify().
• Documentation: Added complete AsciiDoc tutorial under docs/modules/ROOT/pages/modulith-events.adoc and modulith-events/README.adoc, updated root README.adoc and docs/modules/ROOT/nav.adoc.