Change Duo Chat default final error message to be more friendly

What does this MR do and why?

The previous response from Duo Chat when we were unable to parse the LLM response could be offputting to customers.

Before

I don't see how I can help. Please give better instructions!

After

I am unable to find the answer to your question. Please leave feedback so that I can improve.

MR acceptance checklist

✅

Screenshots or screen recordings

How to set up and validate locally

N/A, it is impossible to force the LLM to be unable to parse without manipulating the code.