Add git imap-get-recipients command

Hi all

I was wondering if it would be acceptable for the maintainers to add a git imap-get-recipients command.

I currently am working on it, and it would be a perl script. It would do a very simple thing, take the message id as an input, and output the To: and Cc: recipients of that message ID.

This can be useful to be used alongwith git-send-email, when you send a v2 and you don't have to type all the sender mails again.

I got inspired to make this when I saw that replying to a v1 in a GUI client was so easy since all the recipients got filled automatically.

I currently am using a basic version of this with the --to-cmd command of git-send-email, but can polish it for git.