Allow config prop annotation processor to find reactive cookie props

See gh-31912

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/web/ServerProperties.java

@@ -323,6 +323,7 @@ public static class Session {
 			@DurationUnit(ChronoUnit.SECONDS)
 			private Duration timeout = Duration.ofMinutes(30);
 
+			@NestedConfigurationProperty
 			private final Cookie cookie = new Cookie();
 
 			public Duration getTimeout() {