Add api cross ref linking (#8275)

Example of how it would show up in our python docs:


![image](https://github.com/langchain-ai/langchain/assets/13333726/0f0a88cc-ba4a-4778-bc47-118c66807f15)


Examples added to the reference docs:

https://api.python.langchain.com/en/wfh-api_crosslink/vectorstores/langchain.vectorstores.chroma.Chroma.html#langchain.vectorstores.chroma.Chroma


![image](https://github.com/langchain-ai/langchain/assets/13333726/dcd150de-cb56-4d42-b49a-a76a002a5a52)

docs/extras/integrations/document_loaders/chatgpt_loader.ipynb

@@ -4,7 +4,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "### ChatGPT Data\n",
+    "# ChatGPT Data\n",
     "\n",
     ">[ChatGPT](https://chat.openai.com) is an artificial intelligence (AI) chatbot developed by OpenAI.\n",
     "\n",

docs/extras/integrations/llms/octoai.ipynb

@@ -5,7 +5,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "## OctoAI Compute Service\n",
+    "# OctoAI Compute Service\n",
     "This example goes over how to use LangChain to interact with `OctoAI` [LLM endpoints](https://octoai.cloud/templates)\n",
     "## Environment setup\n",
     "\n",

docs/extras/integrations/tools/awslambda.ipynb

@@ -5,7 +5,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "## AWS Lambda API"
+    "# AWS Lambda API"
    ]
   },
   {