Use Zep for chat history; auto-summarization, intent extraction

Please consider using [Zep ](https://docs.getzep.com/) as a long-term chat history store. It's increasingly being used for larger Langchain / Langchain.js apps where a more sophisticated approach to chat history memory is required.

A snippet from the project's feature list:
- Fast! Zep's async extractors operate independently of the your chat loop, ensuring a snappy user experience.
- Long-term memory persistence, with access to historical messages irrespective of your summarization strategy.
- Auto-summarization of memory messages based on a configurable message window.
- Hybrid Vector search over memories and metadata, with messages automatically embedded on creation.
- Entity Extractor that extracts named entities and intents from messages and stores them in the message metadata.
- Auto-token counting of memories and summaries, allowing finer-grained control over prompt assembly.

Zep's GitHub repo: https://github.com/getzep/zep

Happy to assist with implementation + questions.