Add release notes for v0.231.0

Author: gustavodiaz7722

docs/release_notes/0.231.0.md

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+# Release v0.231.0
+
+## 🚀 Features
+
+- Add support for vpc.controlPlaneOnPrivateSubnets (#8793)
+
+## 🐛 Bug Fixes
+
+- Grant ec2:DescribeSecurityGroups to the IPv6 VPC CNI role (#8837)
+
+## 🧰 Maintenance
+
+- Update coredns (#8842)
+- Update coredns (#8841)
+- Update nvidia-device-plugin to v0.20.0 (#8840)
+
+## Acknowledgments
+
+The eksctl maintainers would like to sincerely thank @guessi, @gustavodiaz7722 and @michaelbeaumont.
+