add workflow to copy conda-forge releases to repo releases

[jaimergp]

Description

I was doing this manually but it's better if this is done in public CI for provenance and transparency.

Checklist - did you ...

• Add a file to the news directory (using the template) for the next release's release notes?
• Add / update necessary tests?
• Add / update outdated documentation?

[marcoesters]

LGTM, even though I personally prefer not to use cd. That way, there is no need to keep track from where commands are called. However, this is a style question, so not a blocker.

[jezdez]

I was just pointed out that this is being done, which I find troubling given that conda-forge is a lot less secure compared to reviewed releases. Given conda-standalone's fundamental position in the conda stack, this change would have needed a security minded review.