Fix for Couchbase Cluster Documentation - PR Ready for Review

[PSriVarshan]

Hi everyone! 👋

I came across an issue in the Spring AI documentation where the Couchbase Cluster bean example was missing a return statement. This caused a compilation error.

🔹 Issue: #2556
🔹 Pull Request (PR): #2557

The fix ensures the method correctly returns a Cluster instance, preventing compilation errors. If any maintainers or community members can review it, that would be great! 🚀

Looking forward to feedback. Thanks! 🙌