docs: Indicated Guardrails for Amazon Bedrock preview status (#16769)

Added notification about limited preview status of Guardrails for Amazon
Bedrock feature to code example.

---------

Co-authored-by: Piyush Jain <piyushjain@duck.com>

docs/docs/integrations/llms/bedrock.ipynb

@@ -111,8 +111,11 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "### Guardrails for Amazon Bedrock example \n",
+   
     "\n",
+    "## Guardrails for Amazon Bedrock (Preview) \n",
+    "[Guardrails for Amazon Bedrock](https://aws.amazon.com/bedrock/guardrails/) evaluates user inputs and model responses based on use case specific policies, and provides an additional layer of safeguards regardless of the underlying model. Guardrails can be applied across models, including Anthropic Claude, Meta Llama 2, Cohere Command, AI21 Labs Jurassic, and Amazon Titan Text, as well as fine-tuned models.\n",
+    "**Note**: Guardrails for Amazon Bedrock is currently in preview and not generally available. Reach out through your usual AWS Support contacts if you’d like access to this feature.\n",
     "In this section, we are going to set up a Bedrock language model with specific guardrails that include tracing capabilities.   "
    ]
   },