Adds ArchUnit as an explicit dependency to spring-modulith-runtime. Registers auto-configuration that throws an exception in case ArchUnit is missing from the classpath (as it is likely that it's declared as test scope dependency only) and a corresponding failure analyzer to give guidance on how to solve the problem.
Application modules can now declare instances of ApplicationModuleInititalizer to execute code upon an ApplicationStartedEvent.
This is achieved by registering a corresponding ApplicationListener in SpringModulithRuntimeAutoConfiguration to invoke all instances of AMI sorted via the Comparator introduced in GH-102. To make sure that the invocation order follows topological order, the runtime module strongly depends on JGraphT.
Introduce Spring Modulith Actuator module to expose the application module structure as Spring Boot actuator. This required a Spring Modulith Runtime module to be extracted from the Spring Modulith Observability one. The former now contains the auto-configured ApplicationRuntime and ApplicationModulesRuntime bean instances to be able to bootstrap a ApplicationModules asynchronously on application startup. The actuator module then contains a Spring Boot @Endpoint implementation consuming the ApplicationModules to render JSON describing the application module structure.
