Document how to add metadata for collection and enum default values

Closes gh-12874

Author: mbhave

spring-boot-project/spring-boot-docs/src/main/asciidoc/appendix-configuration-metadata.adoc

@@ -814,6 +814,51 @@ special handling for collection types (that is detected even if only a getter is
 The annotation processor also supports the use of the `@Data`, `@Getter`, and `@Setter`
 lombok annotations.
 
+
+The annotation processor cannot auto-detect default values for ``Enum``s and ``Collections``s.
+In the cases where a `Collection` or `Enum` property has a non-empty default value,
+<<configuration-metadata-additional-metadata,manual metadata>> should be provided.
+
+Consider the following class:
+
+[source,java,indent=0,subs="verbatim,quotes,attributes"]
+----
+	@ConfigurationProperties(prefix="rabbit")
+	public class RabbitProperties {
+
+		private List<String> addresses = new ArrayList<>(Arrays.asList("a", "b")) ;
+
+		private ContainerType  = ContainerType.SIMPLE;
+
+		// ... getter and setters
+
+		public enum ContainerType {
+
+			SIMPLE,
+
+			DIRECT
+
+		}
+
+	}
+----
+
+In order to document default values for properties in the class above, you could add the following
+JSON to <<configuration-metadata-additional-metadata,the manual metadata of the module>>:
+
+[source,json,indent=0]
+----
+	{
+		"name": "rabbit.addresses",
+		"defaultValue": "a, b"
+	},
+	{
+		"name": "rabbit.container-type",
+		"defaultValue": "simple"
+	}
+----
+
+
 [NOTE]
 ====
 If you are using AspectJ in your project, you need to make sure that the annotation