Update changelog based on model updates

Author: aws-sdk-python-automation

.changes/next-release/api-change-apigateway-8315.json

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+{
+  "type": "api-change",
+  "category": "``apigateway``",
+  "description": "This release adds RootResourceId to GetRestApi response."
+}

.changes/next-release/api-change-ec2-92300.json

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+{
+  "type": "api-change",
+  "category": "``ec2``",
+  "description": "Marking fields as sensitive on BundleTask and GetPasswordData"
+}

.changes/next-release/api-change-polly-442.json

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+{
+  "type": "api-change",
+  "category": "``polly``",
+  "description": "Amazon Polly adds 1 new voice - Zayd (ar-AE)"
+}