feat: introduce the OpenlayerHandler, which implements the LangChain …

[gustavocidornelas]

…callback handler interface

Summary

• Introduces the OpenlayerHandler, which implements the LangChain callback handler interface.
• To use the callback handler, simply set the environment variables (OPENAI_API_KEY, OPENLAYER_API_KEY, OPENLAYER_INFERENCE_PIPELINE_ID) and:

import { HumanMessage } from '@langchain/core/messages';
import { ChatOpenAI } from '@langchain/openai';
import { OpenlayerHandler } from 'openlayer/integrations/langchainCallback';

async function main() {
  const handler = new OpenlayerHandler();

  const model = new ChatOpenAI({
    model: 'gpt-3.5-turbo',
    callbacks: [handler],
  });

  const response = await model.invoke([new HumanMessage({ content: "What's up?" })]);
  return response;
}

main().catch(console.error);