Add changelog

Author: RanVaknin

.changes/next-release/bugfix-AWSSDKforJavav2-1a353a6.json

@@ -0,0 +1,6 @@
+{
+    "type": "bugfix",
+    "category": "AWS SDK for Java v2",
+    "contributor": "",
+    "description": "Optimized JSON serialization by skipping null field marshalling for payload fields"
+}