Document that WRITE_DURATIONS_AS_TIMESTAMPS is disabled by default

Closes gh-38083

Author: wilkinsona

spring-boot-project/spring-boot-docs/src/docs/asciidoc/howto/spring-mvc.adoc

@@ -60,6 +60,7 @@ The `ObjectMapper` (or `XmlMapper` for Jackson XML converter) instance (created
 * `MapperFeature.DEFAULT_VIEW_INCLUSION` is disabled
 * `DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES` is disabled
 * `SerializationFeature.WRITE_DATES_AS_TIMESTAMPS` is disabled
+* `SerializationFeature.WRITE_DURATIONS_AS_TIMESTAMPS` is disabled
 
 Spring Boot also has some features to make it easier to customize this behavior.