[Proposal] Pass additional metadata to sendemail-validate hook from git send-email

Hi,

I was hoping to put a feature proposal forward for git send-email.

For git send-email there is a git hook, sendemail-validate which gets the body of the email that will be sent but is missing some of the metadata that git send-email has access to. I propose that we also pass the extra metadata that gets presented to the user later on via stdout such as: From, To, Cc, Subject, Date, Message-Id, X-Mailer, MIME-Version, Content-Transfer-Encoding to the git hook.

I'm willing to work on the patch but want to make sure the idea would be accepted first.

Thank you, Michael