update CHANGELOG for new user/bot turn start strategies

changelog/3045.added.md

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+- Introducing user and bot turn start strategies. Turn start strategies indicate when user and bot turns begin. In conversational agents, these are often referred to as start/stop speaking or turn-taking plans or policies.
+
+  User turn start strategies indicate when the user starts speaking (e.g. using VAD events or when a user says one or more words).
+
+  Bot turn start strategies indicate when the bot should start speaking (e.g. using an end-of-turn detection model or by observing incoming transcriptions).
+
+  A list of strategies can be specified for both the user and the bot; strategies are evaluated in order until one evaluates to true.
+
+  Available user turn start strategies:
+    - VADUserTurnStartStrategy
+    - TranscriptionUserTurnStartStrategy
+    - MinWordsUserTurnStartStrategy
+
+  Available bot turn start strategies:
+    - TranscriptionBotTurnStartStrategy
+    - TurnAnalyzerBotTurnStartStrategy
+
+  The default strategies are:
+
+    - user: [VADUserTurnStartStrategy, TranscriptionUserTurnStartStrategy]
+    - bot: [TranscriptionBotTurnStartStrategy]
+
+  Turn start strategies are configured when setting up a `PipelineTask`. For example:
+
+  ```python
+  task = PipelineTask(..., params=PipelineParams(
+      turn_start_strategies=TurnStartStrategies(
+          bot=[
+              TurnAnalyzerBotTurnStartStrategy(
+                  turn_analyzer=LocalSmartTurnAnalyzerV3(params=SmartTurnParams())
+              )
+          ],
+      ),
+  ))
+  ```
+
+  In order to use the turn start strategies you should update to the new universal `LLMContext` and `LLMContextAggregatorPair`.