Add support for Agentic Duo Chat code explain evaluations

What does this merge request do and why?

This MR adds support for evaluating Agentic Duo Chat's code explain functionality. It enables testing and validation of the agentic chat feature's ability to explain code through automated evaluations.

Experiments:

• With the existing grep command:
  • Traces
  • Metrics
• With the updated grep command:
  • Traces
  • Metrics

How to set up and validate locally

Please, follow the updated docs.

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.