Support for LangChain 0.2

[bherta]

Context

We want to use this package for its ability to invoke the LLM, but we also want to make use of LangChain 0.2 in our application. Currently this package requires LangChain 0.1. We are able to get around this by forcing LangChain 0.2 via pip, but it would be great if ibm-generative-ai could update to the newer version of LangChain.