Add clipboard copy option (like xclip -selection c)

[n3tw0rth]

It would be really convenient if skate supported an option to automatically copy the output to the clipboard.

For example:

skate get secret -c

This would behave similarly to xclip -selection c, allowing users to copy the retrieved value directly without additional piping or manual steps.

I think this could be a useful quality-of-life improvement for quick secret retrievals.
I already have a small working implementation for this feature and can raise a PR if the maintainers think it’s a good addition.