Update changelog based on model updates

Author: aws-sdk-python-automation

.changes/next-release/api-change-appstream-35569.json

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+{
+  "type": "api-change",
+  "category": "``appstream``",
+  "description": "G6f instance support for AppStream 2.0"
+}

.changes/next-release/api-change-cloudwatch-87469.json

@@ -0,0 +1,5 @@
+{
+  "type": "api-change",
+  "category": "``cloudwatch``",
+  "description": "Fix default dualstack FIPS endpoints in AWS GovCloud(US) regions"
+}

.changes/next-release/api-change-dax-4656.json

@@ -0,0 +1,5 @@
+{
+  "type": "api-change",
+  "category": "``dax``",
+  "description": "This release adds support for IPv6-only, DUAL_STACK DAX instances"
+}

.changes/next-release/api-change-endpointrules-20559.json

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+{
+  "type": "api-change",
+  "category": "``endpoint-rules``",
+  "description": "Update endpoint-rules command to latest version"
+}

.changes/next-release/api-change-kms-93386.json

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+{
+  "type": "api-change",
+  "category": "``kms``",
+  "description": "Documentation only updates for KMS."
+}

.changes/next-release/api-change-neptune-71659.json

@@ -0,0 +1,5 @@
+{
+  "type": "api-change",
+  "category": "``neptune``",
+  "description": "Doc-only update to address customer use."
+}