Add changelog

Author: RanVaknin

.changes/next-release/feature-AmazonDynamoDBEnhancedClient-15a5c11.json

@@ -0,0 +1,6 @@
+{
+    "type": "feature",
+    "category": "Amazon DynamoDB Enhanced Client",
+    "contributor": "",
+    "description": "Improved performance of UpdateExpression conversion by replacing Stream.concat chains and String.format with direct iteration and StringJoiner."
+}