Feature request: trailers mode for contributors

[samueltardieu]

As a contributor to some software using lore, such as QEMU, I'd like to use b4 to gather the trailers to add to the next version of my contribution. However, b4 insists for putting my own Signed-Off-By: at the end, while I'd like to append newly found trailers to the existing list without changing the order.

It would be great to have an option and a configuration entry to tell b4 not to special case the sob trailer.