Add ability to provide text explanations with feedback

[zacps]

We use a self-hosted instance of chat-ui to host a number of foundation models, as well as a few in-house RAG models. In the later case, it's extremely useful for us to be able to gather feedback about problems like hallucination or retrieval failures.

However, the current feedback mechanism only allows a binary thumbs up/down, and doesn't allow users to provide more detail in their response, like what part of it was incorrect, or where in the underlying knoweldge-base the correct answer could be found.

I would love it if when you pressed thumbs up/down it was possible to enter a short text description which would be stored in the database.