Restore configuration metadata for spring.web.resources.chain.enabled

See b6e4533296

core/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/web/WebProperties.java

@@ -188,7 +188,7 @@ public class WebProperties {
 				return this.customized || getStrategy().hasBeenCustomized();
 			}
 
-			public void setEnabled(boolean enabled) {
+			public void setEnabled(Boolean enabled) {
 				this.enabled = enabled;
 				this.customized = true;
 			}