A possibly useful hook for detecting non-GPG-signed commits

Some projects require GPG-signing all your commits. From a security perspective, this is verified by the server. It's easy to configure your `git` client to GPG-sign all your commits by default. **But** some tools don't support GPG-signing (for example, my beloved [GitUp](https://github.com/git-up/GitUp)). It's trickier than it sounds to add GPG signing to some tools, it appears... I often find myself in a situation where I finish some work, create a PR using the `gh` CLI tool (knowing that it'll take some time to run the tests and the whole CI pipeline), then switch context (focus on some other work). 15 minutes later, I switch contexts again, check on the PR, the tests succeeded, **but** the system says "there are some unsigned commits". So I think that it would be useful to actually have a local (even personal, global) way to prevent pushes with unsigned commits, so people can catch such situations very early (and re-sign commits, I actually have a script that does it in one go). It's language-agnostic, so I think it could live in this repo. What do you think? Do you have some feedback? Do you agree it's suitable for this repo, or is it too niche a use case in your opinion?