Update how to evaluate issues/epics against a local duo-chat instance

What does this merge request do and why?

Add docs on how to run the evaluation against a local instance of duo-chat. This process is also described in this video https://drive.google.com/file/d/1X6CARf0gebFYX4Rc9ULhcfq9LLLnJ_O-/view.

Ref. gitlab-org/gitlab#444948 (comment 1831663776).

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

Merge request checklist

• I've ran the affected pipeline(s) to validate that nothing is broken.
• Tests added for new functionality. If not, please raise an issue to follow up.
• Documentation added/updated, if needed.