update-review use EDITOR/editor

[LecrisUT]

Right now when you run fbrnch update-review you can only customize the "Summary". But I would want to put in more detailed comments there, e.g. for rust packages I put the full rust2rpm.toml and *-fix-metadata.diff so that others can replicate locally or confirm I didn't upload an outdated srpm by mistake.

It would be nice if instead of a prompt, you would be put in an editor environment with the Spec, SRPM lines pre-populated so the user can freely edit the message. Like how git commit -s works.

[juhp]

Using an editor seems frequent requested feature: I will try to do that in the next version