[Feature request] Add the ability to rename stashes

[zachhardesty7]

I have a handful of pretty old stashes that I forgot to add a custom name to. I'd love to be able to change their names without losing the original commits dates and diffs. A further idea would be to add support for dropping individual files from a stash. Not sure how difficult either of these are with git, but I imagine it's possible.

Love this extension by the way, use it every day. Thanks!

(Side note: I'm not opposed to helping work on this feature if I had your support. I have a couple of simple-ish extensions in the marketplace, so I'm familiar with the VSCode APIs.)