Support for Markdown as an output format or via Copy button

[svrnm]

Upstreaming this feature request from opentelemetry.io repo issue open-telemetry/opentelemetry.io#8146 from @yaten2302:

Desired feature or idea: Currently [...] there's no opt to copy the entire page as markdown which can be easily be passed as a prompt to tools like ChatGPT, Gemini etc... And the user can easily ask questions based on that (since then it would have the entire context).

Additional context: This feature is similar to clerk docs (at the bottom right).

Comment from @chalin:

Hugo has new features in support of this. Might be a good addition for Docsy.

[chalin]

I've generalized this to also cover "support for Markdown as an output format". /cc @vitorvasc