[Docs] Add changelog entry for 3.9.3: cloud_dns.

[gmarciani]

Description of changes

[Docs] Add changelog entry for 3.9.3: cloud_dns.

Tests

Not needed.

References

• Link to impacted open issues.
• Link to related PRs in other packages (i.e. cookbook, node).
• Link to documentation useful to understand the changes.

Checklist

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• Check all commits' messages are clear, describing what and why vs how.
• Make sure to have added unit tests or integration tests to cover the new/modified code.
• Check if documentation is impacted by this change.

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