doc: CHANGELOG update

Author: JPPortier

CHANGELOG.md

@@ -16,6 +16,19 @@ All notable changes to the **Sinch Java SDK** are documented in this file.
 
 ---
 
+## v2.1 – unreleased
+
+### SDK
+- **[fix]** `HttpClientApache`: declare now `headersToBeAdded` as `volatile` to guarantee visibility across threads in concurrent usage
+- **[fix]** `HttpClientApache`: wrap response-body `Scanner` in a try-with-resources block to prevent resource leaks; gracefully handle empty (`null`) response entities
+- **[fix]** `SinchClient`: guard against a `NullPointerException` when `java.vendor` system property is absent while building the `User-Agent` auxiliary flag
+- **[fix]** `Configuration`: correct copy-paste error in `toString()` and Javadoc — `conversationContext` label was incorrectly attributed to the Voice domain
+
+### Examples / Snippets
+- **[doc]** Fix typos in `conversation/conversations/Create` and `voice/applications/GetEventDestinations` snippets
+
+---
+
 ## v2.0 – 2026-03-31
 
 ### Major breaking changes with major release