Update changelog based on model updates

Author: aws-sdk-python-automation

.changes/next-release/api-change-codestarconnections-56163.json

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+{
+  "type": "api-change",
+  "category": "``codestar-connections``",
+  "description": "This release updates a few CodeStar Connections related APIs."
+}

.changes/next-release/api-change-docdb-11820.json

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+{
+  "type": "api-change",
+  "category": "``docdb``",
+  "description": "Amazon DocumentDB updates for new cluster storage configuration: Amazon DocumentDB I/O-Optimized."
+}

.changes/next-release/api-change-ec2-43138.json

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+{
+  "type": "api-change",
+  "category": "``ec2``",
+  "description": "This release adds support for Security group referencing over Transit gateways, enabling you to simplify Security group management and control of instance-to-instance traffic across VPCs that are connected by Transit gateway."
+}