AgentChat task message type and group chat state validation for Swarm (#4230)

* task can be ChatMessage; add group chat state validation step, and address swarm state valiation; change handling of start and reset to RPC to capture any error.

* Update tutorial note

python/packages/autogen-core/docs/src/user-guide/agentchat-user-guide/tutorial/teams.ipynb

@@ -764,16 +764,6 @@
     "# Use `asyncio.run(Console(lazy_agent_team.run_stream(task=\"It is raining in New York.\")))` when running in a script.\n",
     "await Console(lazy_agent_team.run_stream(task=\"It is raining in New York.\"))"
    ]
-  },
-  {
-   "cell_type": "markdown",
-   "metadata": {},
-   "source": [
-    "```{note}\n",
-    "Currently the handoff termination approach does not work with {py:class}`~autogen_agentchat.teams.Swarm`.\n",
-    "Please stay tuned for the updates.\n",
-    "```"
-   ]
   }
  ],
  "metadata": {
@@ -792,7 +782,7 @@
    "name": "python",
    "nbconvert_exporter": "python",
    "pygments_lexer": "ipython3",
-   "version": "3.12.6"
+   "version": "3.11.5"
   }
  },
  "nbformat": 4,