Update CHANGELOG.md (#34343)

### Packages impacted by this PR
@azure/cosmos

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### Describe the problem that is addressed by this PR
This PR marks a feature as preview in CHANGELOG

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there are more than one possible design, why was the one in this PR
chosen?


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- [ ] Added impacted package name to the issue description
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- [ ] Added a changelog (if necessary)

Author: amanrao23

sdk/cosmosdb/cosmos/CHANGELOG.md

@@ -4,7 +4,7 @@
 ## 4.4.0 (2025-05-13)
 
 ### Features Added
-#### New Bulk API
+#### New Bulk API (Preview)
 The new `executeBulkOperations` API in the SDK brings significant enhancements for bulk workloads. It removes the previous 100-operation limit, adds operation-level retries for improved resilience, and introduces dynamic congestion control to optimize performance based on real-time system feedback.
 
 Example of using `executeBulkOperations`: