Allow Copilot to save/export conversation

[overnichenko]

It is basic ability that is availble in most popular applications (including natove Copilot), but somehow is not supported by PowerBI copilot. Sometimes we need to share the results of copilot investigation, discuss it or just save for a future references. But currently the only option is to copy/paste the content manually which is very inconvenient. Export to PDF or at least JSON will be much better.