Make PRODUCTION_RUNTIME_CLASSPATH_NAME public

Change `SpringBootPlugin.PRODUCTION_RUNTIME_CLASSPATH_NAME` from package
private to public so that it can be accessed in user build scripts.

Fixes gh-26686

Author: philwebb

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/src/main/java/org/springframework/boot/gradle/plugin/SpringBootPlugin.java

@@ -76,7 +76,11 @@ public class SpringBootPlugin implements Plugin<Project> {
 	 */
 	public static final String DEVELOPMENT_ONLY_CONFIGURATION_NAME = "developmentOnly";
 
-	static final String PRODUCTION_RUNTIME_CLASSPATH_NAME = "productionRuntimeClasspath";
+	/**
+	 * The name of the {@code productionRuntimeClasspath} configuration.
+	 * @since 2.4.7
+	 */
+	public static final String PRODUCTION_RUNTIME_CLASSPATH_NAME = "productionRuntimeClasspath";
 
 	/**
 	 * The coordinates {@code (group:name:version)} of the