Polish DEFAULT_SERVICE_NAME javadoc

See gh-44494

Author: philwebb

spring-boot-project/spring-boot-actuator-autoconfigure/src/main/java/org/springframework/boot/actuate/autoconfigure/opentelemetry/OpenTelemetryResourceAttributes.java

@@ -44,7 +44,8 @@
 public final class OpenTelemetryResourceAttributes {
 
 	/**
-	 * Default value for service name if {@code service.name} is not set.
+	 * Default value for service name. Used if {@code service.name} is not set and no name
+	 * can be deduced from the running application.
 	 */
 	private static final String DEFAULT_SERVICE_NAME = "unknown_service";