Add ability to copy message references from Web App

[debanjum]

Background

Khoj currently supports ability to copy chat messages. But you cannot easily copy references used by Khoj to generate responses.

Feature

• Add a copy references button to top of the references pane which opens when the "View references" link is clicked at the bottom of each Khoj chat response.
• This should copy all the reference web page and file path links as a markdown bullet list. For example:

  - [2024 - Wikipedia](https://en.wikipedia.org/wiki/2024)
  - [2023 - Wikipedia](https://en.wikipedia.org/wiki/2023)