Re-use chains

[jeremymanning]

Overview

Instead of creating a new chain with each prompt, we should create the chain once (maybe when the chatify extension is first loaded?) and re-use it to respond to each query.

Completion criteria

This requires refactoring this function and this function

• create a new chain when the extension is first loaded
• execute the chain when new queries are submitted

Resources (optional)

Mentioned here.