changing/adding details for new metrics etcd_mvcc_db_total_size_in_bytes and etcd_mvcc_db_total_size_in_use_in_bytes

cr: https://code.amazon.com/reviews/CR-267351160

Author: Prabhat Saxena

latest/ug/observability/cloudwatch.adoc

@@ -252,8 +252,15 @@ https://kubernetes.io/docs/concepts/cluster-administration/flow-control/[feature
 
 *Valid statistics:* Average
 
-|`apiserver_storage_size_bytes`
-|The physical size in bytes of the etcd storage database file used by the API servers in the cluster. This metric represents the actual disk space allocated for the storage.
+|`etcd_mvcc_db_total_size_in_bytes`
+|Total size of the underlying database physically allocated in bytes.  Note that this metric measures physical disk allocation and is not used for quota enforcement. (also known as apiserver_storage_size_bytes) 
+
+*Units:* Bytes
+
+*Valid statistics:* Maximum
+
+|`etcd_mvcc_db_total_size_in_use_in_bytes`
+|The actual data size of the etcd database, excluding free space waiting for defragmentation. This metric indicates the current database usage and determines whether the cluster will exceed the database size quota and enter read-only mode.
 
 *Units:* Bytes