Neptune graph and openCypher QA Chain (#8035)

## Description
This PR adds a graph class and an openCypher QA chain to work with the
Amazon Neptune database.

## Dependencies
`requests` which is included in the LangChain dependencies.

## Maintainers for Review
@krlawrence
@baskaryan

### Twitter handle
pjain7

docs/extras/modules/chains/additional/neptune_cypher_qa.ipynb

@@ -0,0 +1,52 @@
+{
+ "cells": [
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "# Neptune Open Cypher QA Chain\n",
+    "This QA chain queries Neptune graph database using openCypher and returns human readable response\n"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "from langchain.graphs.neptune_graph import NeptuneGraph\n",
+    "\n",
+    "\n",
+    "host = \"<neptune-host>\"\n",
+    "port = 80\n",
+    "use_https = False\n",
+    "\n",
+    "graph = NeptuneGraph(host=host, port=port, use_https=use_https)"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "from langchain.chat_models import ChatOpenAI\n",
+    "from langchain.chains.graph_qa.neptune_cypher import NeptuneOpenCypherQAChain\n",
+    "\n",
+    "llm = ChatOpenAI(temperature=0, model=\"gpt-4\")\n",
+    "\n",
+    "chain = NeptuneOpenCypherQAChain.from_llm(llm=llm, graph=graph)\n",
+    "\n",
+    "chain.run(\"how many outgoing routes does the Austin airport have?\")"
+   ]
+  }
+ ],
+ "metadata": {
+  "language_info": {
+   "name": "python"
+  },
+  "orig_nbformat": 4
+ },
+ "nbformat": 4,
+ "nbformat_minor": 2
+}