Add azure cognitive search retriever (#4467)

All credit to @UmerHA, made a couple small changes

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Co-authored-by: UmerHA <40663591+UmerHA@users.noreply.github.com>

docs/modules/indexes/retrievers/examples/azure-cognitive-search-retriever.ipynb

@@ -0,0 +1,128 @@
+{
+ "cells": [
+  {
+   "cell_type": "markdown",
+   "id": "1edb9e6b",
+   "metadata": {},
+   "source": [
+    "# Azure Cognitive Search Retriever\n",
+    "\n",
+    "This notebook shows how to use Azure Cognitive Search (ACS) within LangChain."
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "074b0004",
+   "metadata": {},
+   "source": [
+    "## Set up Azure Cognitive Search\n",
+    "\n",
+    "To set up ACS, please follow the instrcutions [here](https://learn.microsoft.com/en-us/azure/search/search-create-service-portal).\n",
+    "\n",
+    "Please note\n",
+    "1. the name of your ACS service, \n",
+    "2. the name of your ACS index,\n",
+    "3. your API key.\n",
+    "\n",
+    "Your API key can be either Admin or Query key, but as we only read data it is recommended to use a Query key."
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "0474661d",
+   "metadata": {},
+   "source": [
+    "## Using the Azure Cognitive Search Retriever"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 10,
+   "id": "39d6074e",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "import os\n",
+    "\n",
+    "from langchain.retrievers import AzureCognitiveSearchRetriever"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "b7243e6d",
+   "metadata": {},
+   "source": [
+    "Set Service Name, Index Name and API key as environment variables (alternatively, you can pass them as arguments to `AzureCognitiveSearchRetriever`)."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "id": "33fd23d1",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "os.environ[\"AZURE_COGNITIVE_SEARCH_SERVICE_NAME\"] = \"<YOUR_ACS_SERVICE_NAME>\"\n",
+    "os.environ[\"AZURE_COGNITIVE_SEARCH_INDEX_NAME\"] =\"<YOUR_ACS_INDEX_NAME>\"\n",
+    "os.environ[\"AZURE_COGNITIVE_SEARCH_API_KEY\"] = \"<YOUR_API_KEY>\""
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "057deaad",
+   "metadata": {},
+   "source": [
+    "Create the Retriever"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "id": "c18d0c4c",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "retriever = AzureCognitiveSearchRetriever(content_key=\"content\")"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "e94ea104",
+   "metadata": {},
+   "source": [
+    "Now you can use retrieve documents from Azure Cognitive Search"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "id": "c8b5794b",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "retriever.get_relevant_documents(\"what is langchain\")"
+   ]
+  }
+ ],
+ "metadata": {
+  "kernelspec": {
+   "display_name": "Python 3 (ipykernel)",
+   "language": "python",
+   "name": "python3"
+  },
+  "language_info": {
+   "codemirror_mode": {
+    "name": "ipython",
+    "version": 3
+   },
+   "file_extension": ".py",
+   "mimetype": "text/x-python",
+   "name": "python",
+   "nbconvert_exporter": "python",
+   "pygments_lexer": "ipython3",
+   "version": "3.11.3"
+  }
+ },
+ "nbformat": 4,
+ "nbformat_minor": 5
+}