Update changelog based on model updates

Author: aws-sdk-python-automation

.changes/next-release/api-change-mediapackage-15340.json

@@ -0,0 +1,5 @@
+{
+  "type": "api-change",
+  "category": "``mediapackage``",
+  "description": "This release adds Ads AdTriggers and AdsOnDeliveryRestrictions to describe calls for CMAF endpoints on MediaPackage."
+}

.changes/next-release/api-change-rds-34559.json

@@ -0,0 +1,5 @@
+{
+  "type": "api-change",
+  "category": "``rds``",
+  "description": "Removes support for RDS Custom from DBInstanceClass in ModifyDBInstance"
+}