I'm asking because while I've used SSH keys for my own work before, I've never done anything with anyone else's keys. I don't want to write a tool that accidentally does something dangerous with the user's key.
If this is a reasonable workflow, I'll add support for generating a new key pair if a suitable key is not found. I'll also remove the `--key-assist` flag, and this will just be the normal workflow when the user has not already uploaded a key to Scalingo.