Update changelog based on model updates

Author: aws-sdk-python-automation

.changes/next-release/api-change-opensearchserverless-62767.json

@@ -0,0 +1,5 @@
+{
+  "type": "api-change",
+  "category": "``opensearchserverless``",
+  "description": "This release includes two new exception types \"ServiceQuotaExceededException\" and \"OcuLimitExceededException\"."
+}

.changes/next-release/api-change-rds-20481.json

@@ -0,0 +1,5 @@
+{
+  "type": "api-change",
+  "category": "``rds``",
+  "description": "Add support for creating a read replica DB instance from a Multi-AZ DB cluster."
+}