feat: Copy button for code block

[hahuyhoang411]

Problem
We haven't had a copy button for the code block yet. The only way to copy is copy the whole message.

Success Criteria
Only copy the text between triple backticks (```)

Additional context
The example of copy button:

[freelerobot]

From my issue:

Problem
Users can't easily copy code answers

Success Criteria
A clear and concise description of what you want to happen.

LLM responds with a code block
User hovering over codeblock should see option to copy codeblock
Clicking copy, copies only the code, not the entire LLM response.
Additional context
Add any other context or screenshots about the feature request here.