Enable signing commits via SSH keys

GitLab 15.7+ supports using SSH keys to automatically sign pushed commits, c.f. https://docs.gitlab.com/ee/user/project/repository/ssh_signed_commits/ We should enable this once this is deployed on OpenCoDE. This should be especially useful once we have distributed hardware tokens managing these SSH keys.

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information