docs: IBM watsonx.ai Use invoke instead of __call__ (#16371)

- **Description:** Updating documentation of IBM
[watsonx.ai](https://www.ibm.com/products/watsonx-ai) LLM with using
`invoke` instead of `__call__`
- **Dependencies:**
[ibm-watsonx-ai](https://pypi.org/project/ibm-watsonx-ai/),
  - **Tag maintainer:** : 

Please make sure your PR is passing linting and testing before
submitting. Run `make format`, `make lint` and `make test` to check this
locally. ✅

The following warning information show when i use `run` and `__call__`
method:
```
LangChainDeprecationWarning: The function `__call__` was deprecated in LangChain 0.1.7 and will be removed in 0.2.0. Use invoke instead.
  warn_deprecated(
```

We need to update documentation for using `invoke` method

docs/docs/integrations/llms/watsonxllm.ipynb

@@ -176,7 +176,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 4,
+   "execution_count": 3,
    "id": "c7d80c05",
    "metadata": {},
    "outputs": [],
@@ -197,17 +197,18 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 5,
+   "execution_count": 4,
    "id": "dc076c56",
    "metadata": {},
    "outputs": [
     {
      "data": {
       "text/plain": [
-       "'How many breeds of dog are there?'"
+       "{'topic': 'dog',\n",
+       " 'text': 'What is the name of the dog that is the most popular in the world?'}"
       ]
      },
-     "execution_count": 5,
+     "execution_count": 4,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -216,7 +217,7 @@
     "from langchain.chains import LLMChain\n",
     "\n",
     "llm_chain = LLMChain(prompt=prompt, llm=watsonx_llm)\n",
-    "llm_chain.run(\"dog\")"
+    "llm_chain.invoke(\"dog\")"
    ]
   },
   {
@@ -248,7 +249,7 @@
    "source": [
     "# Calling a single prompt\n",
     "\n",
-    "watsonx_llm(\"Who is man's best friend?\")"
+    "watsonx_llm.invoke(\"Who is man's best friend?\")"
    ]
   },
   {
@@ -327,7 +328,7 @@
    "name": "python",
    "nbconvert_exporter": "python",
    "pygments_lexer": "ipython3",
-   "version": "3.9.18"
+   "version": "3.10.13"
   }
  },
  "nbformat": 4,