Stack rebase needs GPG signing support to be truly usable

[aleksei-averchenko-wise]

Right now, GitHub's rebase button results in the rewritten commits having no GPG signatures, which makes it inconvenient to use. Please consider adding commit signing support via GitHub

[raulgg]

This behavior is noted in the documentation, so I assume it is intentional at the moment.

However, I think commit signing in server-side rebasing is a must. I've been using stacked PRs with other tools such as Graphite for a while, and server-side rebasing was able to properly sign the commits by using a key configured in their settings. I'm missing that in GitHub's native stacks.