Add release notes for v0.229.0 (#8776)

Co-authored-by: michaelhtm <98621731+michaelhtm@users.noreply.github.com>

Author: eksctl-bot

docs/release_notes/0.229.0.md

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+# Release v0.229.0
+
+## 🚀 Features
+
+- Add cluster version rollback support with rollbackConfig (#8780)
+- Add support for EKS on Outposts with EC2 instance store (#8774)
+
+## Acknowledgments
+
+The eksctl maintainers would like to sincerely thank @DimitriPL5 and @michaelhtm.
+