Fix default value of endpoint's cache ttl

Closes spring-projectsgh-12173

Author: snicoll

spring-boot-project/spring-boot-tools/spring-boot-configuration-processor/src/main/java/org/springframework/boot/configurationprocessor/ConfigurationMetadataAnnotationProcessor.java

@@ -438,7 +438,7 @@ private void processEndpoint(AnnotationMirror annotation, TypeElement element) {
 		if (hasMainReadOperation(element)) {
 			this.metadataCollector.add(ItemMetadata.newProperty(endpointKey,
 					"cache.time-to-live", Duration.class.getName(), type, null,
-					"Maximum time that a response can be cached.", 0, null));
+					"Maximum time that a response can be cached.", "0ms", null));
 		}
 	}
 

spring-boot-project/spring-boot-tools/spring-boot-configuration-processor/src/test/java/org/springframework/boot/configurationprocessor/ConfigurationMetadataAnnotationProcessorTests.java

@@ -706,7 +706,7 @@ private Metadata.MetadataItemCondition enabledFlag(String endpointId,
 	private Metadata.MetadataItemCondition cacheTtl(String endpointId) {
 		return Metadata
 				.withProperty("management.endpoint." + endpointId + ".cache.time-to-live")
-				.ofType(Duration.class).withDefaultValue(0)
+				.ofType(Duration.class).withDefaultValue("0ms")
 				.withDescription("Maximum time that a response can be cached.");
 	}