Add a "copy" button to code blocks

[chipzoller]

This (cool, btw) theme is commonly used for documentation of "technical" subject matters which often include code. It would be super helpful if there were just a simple "copy" button somewhere in that code block providing users an easier way to select all and copy what's in that block. We implemented that plus other functions in our Clarity theme, so if no one can pick this up it might be something we could look at doing in the future.

[LisaFC]

If you switch to using Prism for your code highlighting, you'll get a copy button!
https://www.docsy.dev/docs/adding-content/lookandfeel/#code-highlighting-with-prism

(we didn't make Prism the default just because a lot of our users rely on Chroma styles, but it's easy to switch)