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-test/src/main/java/org/springframework/modulith/test/TestApplicationModules.java

@@ -0,0 +1,43 @@
+/*
+ * Copyright 2022 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.springframework.modulith.test;
+
+import java.util.List;
+
+import org.springframework.modulith.model.ApplicationModules;
+import org.springframework.modulith.model.ModulithMetadata;
+
+import com.tngtech.archunit.base.DescribedPredicate;
+import com.tngtech.archunit.core.importer.ImportOption;
+
+/**
+ * Utility methods to work with test {@link ApplicationModules}. <em>Not intended public API!</em>
+ *
+ * @author Oliver Drotbohm
+ */
+public class TestApplicationModules {
+
+	/**
+	 * Creates an {@link ApplicationModules} instance from the given package but only inspecting the test code.
+	 *
+	 * @param basePackage must not be {@literal null} or empty.
+	 * @return
+	 */
+	public static ApplicationModules of(String basePackage) {
+		return new ApplicationModules(ModulithMetadata.of(basePackage), List.of(basePackage),
+				DescribedPredicate.alwaysFalse(), false, new ImportOption.OnlyIncludeTests()) {};
+	}
+}