Restored the 2.13.x-changelog file, which was empty for some reason (aws#6026)

Author: debora-ito

.changes/next-release/bugfix-AWSSDKforJavav2-a52ace4.json

@@ -0,0 +1,6 @@
+{
+    "type": "bugfix",
+    "category": "AWS SDK for Java v2",
+    "contributor": "",
+    "description": "Restored the 2.13.x changelog file."
+}