GH-87 - Expose module structure as actuator endpoint.

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.

spring-modulith-runtime/pom.xml

@@ -0,0 +1,45 @@
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
+	<modelVersion>4.0.0</modelVersion>
+
+	<parent>
+		<groupId>org.springframework.experimental</groupId>
+		<artifactId>spring-modulith</artifactId>
+		<version>0.2.0-SNAPSHOT</version>
+	</parent>
+
+	<name>Spring Modulith - Runtime support</name>
+	<artifactId>spring-modulith-runtime</artifactId>
+
+	<properties>
+		<module.name>org.springframework.modulith.runtime</module.name>
+	</properties>
+
+	<dependencies>
+
+		<dependency>
+			<groupId>org.springframework.experimental</groupId>
+			<artifactId>spring-modulith-core</artifactId>
+			<version>${project.version}</version>
+		</dependency>
+
+		<dependency>
+			<groupId>org.springframework.boot</groupId>
+			<artifactId>spring-boot-autoconfigure</artifactId>
+			<optional>true</optional>
+		</dependency>
+
+		<dependency>
+			<groupId>org.springframework.boot</groupId>
+			<artifactId>spring-boot-starter-test</artifactId>
+			<scope>test</scope>
+		</dependency>
+
+		<dependency>
+			<groupId>org.springframework.boot</groupId>
+			<artifactId>spring-boot-actuator-autoconfigure</artifactId>
+			<scope>test</scope>
+		</dependency>
+
+	</dependencies>
+
+</project>