feat: add the support to delete thread (session)

Author: ksachdeva

adk-chatkit/src/adk_chatkit/_store.py

@@ -202,7 +202,9 @@ async def delete_thread_item(self, thread_id: str, item_id: str, context: ADKCon
         pass
 
     async def delete_thread(self, thread_id: str, context: ADKContext) -> None:
-        raise NotImplementedError()
+        await self._session_service.delete_session(
+            app_name=context["app_name"], user_id=context["user_id"], session_id=thread_id
+        )
 
     async def save_item(self, thread_id: str, item: ThreadItem, context: ADKContext) -> None:
         # we will only handle specify types of items here