docs[patch]: add missing imports for local_llms (langchain-ai#14453)

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Keeping it consistent with everywhere else in the docs and adding the
missing imports to be able to copy paste and run the code example.

---------

Co-authored-by: Erick Friis <[email protected]>

docs/docs/guides/local_llms.ipynb

@@ -284,6 +284,8 @@
    "metadata": {},
    "outputs": [],
    "source": [
+    "from langchain.callbacks.manager import CallbackManager\n",
+    "from langchain.callbacks.streaming_stdout import StreamingStdOutCallbackHandler\n",
     "from langchain.llms import LlamaCpp\n",
     "\n",
     "llm = LlamaCpp(\n",