bin: add rebase mode

when we need to apply trailers to a whole MR at once, it's convenient to
do something like `git rebase --exec "rb faith" origin/main`. This adds that
operation into the script itself, so that can be done with simply
`rb -r origin/main faith`.

Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Reviewed-by: Mel Henning <mhenning@darkrefraction.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/34409>
1 file changed