Add oobabooga/text-generation-webui support as a llm (#5997)

Add oobabooga/text-generation-webui support as an LLM. Currently,
supports using text-generation-webui's non-streaming API interface.
Allows users who already have text-gen running to use the same models
with langchain.

#### Before submitting

Simple usage, similar to existing LLM supported:

```
from langchain.llms import TextGen
llm = TextGen(model_url = "http://localhost:5000")
```
#### Who can review?

 @hwchase17 - project lead

---------

Co-authored-by: Hien Ngo <Hien.Ngo@adia.ae>

docs/modules/models/llms/integrations/textgen.ipynb

@@ -0,0 +1,87 @@
+{
+ "cells": [
+  {
+   "attachments": {},
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "# TextGen\n",
+    "\n",
+    "[GitHub:oobabooga/text-generation-webui](https://github.com/oobabooga/text-generation-webui) A gradio web UI for running Large Language Models like LLaMA, llama.cpp, GPT-J, Pythia, OPT, and GALACTICA.\n",
+    "\n",
+    "This example goes over how to use LangChain to interact with LLM models via the `text-generation-webui` API integration.\n",
+    "\n",
+    "Please ensure that you have `text-generation-webui` configured and an LLM installed.  Recommended installation via the [one-click installer appropriate](https://github.com/oobabooga/text-generation-webui#one-click-installers) for your OS.\n",
+    "\n",
+    "Once `text-generation-webui` is installed and confirmed working via the web interface, please enable the `api` option either through the web model configuration tab, or by adding the run-time arg `--api` to your start command."
+   ]
+  },
+  {
+   "attachments": {},
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Set model_url and run the example"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 1,
+   "metadata": {
+    "tags": []
+   },
+   "outputs": [],
+   "source": [
+    "model_url = \"http://localhost:5000\""
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {
+    "tags": []
+   },
+   "outputs": [],
+   "source": [
+    "import langchain\n",
+    "from langchain import PromptTemplate, LLMChain\n",
+    "from langchain.llms import TextGen\n",
+    "\n",
+    "langchain.debug = True\n",
+    "\n",
+    "template = \"\"\"Question: {question}\n",
+    "\n",
+    "Answer: Let's think step by step.\"\"\"\n",
+    "\n",
+    "\n",
+    "prompt = PromptTemplate(template=template, input_variables=[\"question\"])\n",
+    "llm = TextGen(model_url=model_url)\n",
+    "llm_chain = LLMChain(prompt=prompt, llm=llm)\n",
+    "question = \"What NFL team won the Super Bowl in the year Justin Bieber was born?\"\n",
+    "\n",
+    "llm_chain.run(question)"
+   ]
+  }
+ ],
+ "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": "3.10.7"
+  }
+ },
+ "nbformat": 4,
+ "nbformat_minor": 4
+}