[v16] Edit DynamoDB link in the CHANGELOG

Backports #42569

Linking to a partial won't work in the docs engine we are migrating to.
Instead, link to the sectionof a page that includes the partial.

CHANGELOG.md

@@ -190,7 +190,7 @@ Detailed setup instructions are available in the [documentation](https://github.
 
 Teleport clusters using the DynamoDB backend on AWS now require the
 `dynamodb:ConditionCheckItem` permissions. For a full list of required
-permissions, see the IAM policy [example](https://github.com/gravitational/teleport/blob/branch/v16/docs/pages/includes/dynamodb-iam-policy.mdx).
+permissions, see the IAM policy [example](docs/pages/reference/backends.mdx#dynamodb).
 
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