docs: update IBM WatsonxLLM docs with deprecated LLMChain (#21960)

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- [x] **PR title**: "update IBM WatsonxLLM docs with deprecated
LLMChain"

- [x] **PR message**: 
- **Description:** update IBM WatsonxLLM docs with deprecated LLMChain

- [x] **Lint and test**: Run `make format`, `make lint` and `make test`
from the root of the package(s) you've modified. See contribution
guidelines for more: https://python.langchain.com/docs/contributing/

docs/docs/integrations/llms/ibm_watsonx.ipynb

@@ -24,7 +24,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 4,
+   "execution_count": 1,
    "id": "2f1fff4e",
    "metadata": {},
    "outputs": [],
@@ -45,7 +45,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 1,
+   "execution_count": 2,
    "id": "11d572a1",
    "metadata": {},
    "outputs": [],
@@ -93,7 +93,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 2,
+   "execution_count": 3,
    "id": "407cd500",
    "metadata": {},
    "outputs": [],
@@ -194,6 +194,28 @@
     ")"
    ]
   },
+  {
+   "cell_type": "markdown",
+   "id": "7c4a632b",
+   "metadata": {},
+   "source": [
+    "You can also pass the IBM's [`ModelInference`](https://ibm.github.io/watsonx-ai-python-sdk/fm_model_inference.html) object into `WatsonxLLM` class."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "id": "5335b148",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "from ibm_watsonx_ai.foundation_models import ModelInference\n",
+    "\n",
+    "model = ModelInference(...)\n",
+    "\n",
+    "watsonx_llm = WatsonxLLM(watsonx_model=model)"
+   ]
+  },
   {
    "cell_type": "markdown",
    "id": "c25ecbd1",
@@ -213,6 +235,7 @@
     "from langchain_core.prompts import PromptTemplate\n",
     "\n",
     "template = \"Generate a random question about {topic}: Question: \"\n",
+    "\n",
     "prompt = PromptTemplate.from_template(template)"
    ]
   },
@@ -221,31 +244,32 @@
    "id": "79056d8e",
    "metadata": {},
    "source": [
-    "Provide a topic and run the `LLMChain`."
+    "Provide a topic and run the chain."
    ]
   },
   {
    "cell_type": "code",
-   "execution_count": 10,
+   "execution_count": 9,
    "id": "dc076c56",
    "metadata": {},
    "outputs": [
     {
      "data": {
       "text/plain": [
-       "{'topic': 'dog', 'text': 'Why do dogs howl?'}"
+       "'What is the difference between a dog and a wolf?'"
       ]
      },
-     "execution_count": 10,
+     "execution_count": 9,
      "metadata": {},
      "output_type": "execute_result"
     }
    ],
    "source": [
-    "from langchain.chains import LLMChain\n",
+    "llm_chain = prompt | watsonx_llm\n",
     "\n",
-    "llm_chain = LLMChain(prompt=prompt, llm=watsonx_llm)\n",
-    "llm_chain.invoke(\"dog\")"
+    "topic = \"dog\"\n",
+    "\n",
+    "llm_chain.invoke(topic)"
    ]
   },
   {