Add LLMonitor Callback Handler Integration - open-source observabilit…

…y & analytics (#9870)

Adds support for [llmonitor](https://llmonitor.com) callbacks.

It enables:
- Requests tracking / logging / analytics
- Error debugging
- Cost analytics
- User tracking

Let me know if anythings neds to be changed for merge.

Thank you!

docs/extras/integrations/callbacks/llmonitor.md

@@ -0,0 +1,63 @@
+# LLMonitor
+
+[LLMonitor](https://llmonitor.com) is an open-source observability platform that provides cost tracking, user tracking and powerful agent tracing.
+
+<video controls width='100%' >
+  <source src='https://llmonitor.com/videos/demo-annotated.mp4'/>
+</video>
+
+## Setup
+Create an account on [llmonitor.com](https://llmonitor.com), create an `App`, and then copy the associated `tracking id`.
+Once you have it, set it as an environment variable by running:
+```bash
+export LLMONITOR_APP_ID="..."
+```
+
+If you'd prefer not to set an environment variable, you can pass the key directly when initializing the callback handler:
+```python
+from langchain.callbacks import LLMonitorCallbackHandler
+
+handler = LLMonitorCallbackHandler(app_id="...")
+```
+
+## Usage with LLM/Chat models
+```python
+from langchain.llms import OpenAI
+from langchain.chat_models import ChatOpenAI
+from langchain.callbacks import LLMonitorCallbackHandler
+
+handler = LLMonitorCallbackHandler(app_id="...")
+
+llm = OpenAI(
+    callbacks=[handler],
+)
+
+chat = ChatOpenAI(
+    callbacks=[handler],
+    metadata={"userId": "123"},  # you can assign user ids to models in the metadata
+)
+```
+
+
+## Usage with agents
+```python
+from langchain.agents import load_tools, initialize_agent, AgentType
+from langchain.llms import OpenAI
+from langchain.callbacks import LLMonitorCallbackHandler
+
+handler = LLMonitorCallbackHandler(app_id="...")
+
+llm = OpenAI(temperature=0)
+tools = load_tools(["serpapi", "llm-math"], llm=llm)
+agent = initialize_agent(tools, llm, agent=AgentType.ZERO_SHOT_REACT_DESCRIPTION)
+agent.run(
+    "Who is Leo DiCaprio's girlfriend? What is her current age raised to the 0.43 power?",
+    callbacks=[handler],
+    metadata={
+        "agentName": "Leo DiCaprio's girlfriend",  # you can assign a custom agent in the metadata
+    },
+)
+```
+
+## Support
+For any question or issue with integration you can reach out to the LLMonitor team on [Discord](http://discord.com/invite/8PafSG58kK) or via [email](mailto:vince@llmonitor.com).

libs/langchain/langchain/callbacks/__init__.py

@@ -19,6 +19,7 @@
 from langchain.callbacks.human import HumanApprovalCallbackHandler
 from langchain.callbacks.infino_callback import InfinoCallbackHandler
 from langchain.callbacks.labelstudio_callback import LabelStudioCallbackHandler
+from langchain.callbacks.llmonitor_callback import LLMonitorCallbackHandler
 from langchain.callbacks.manager import (
     collect_runs,
     get_openai_callback,
@@ -54,6 +55,7 @@
     "HumanApprovalCallbackHandler",
     "InfinoCallbackHandler",
     "MlflowCallbackHandler",
+    "LLMonitorCallbackHandler",
     "OpenAICallbackHandler",
     "StdOutCallbackHandler",
     "AsyncIteratorCallbackHandler",