You're not going to be able to avoid that ssh-keygen step.
"Pick a huge random number, this is a private key, you must never tell anybody else this key" is a fundamental operation. If they've never done this operation, that's more telling us how bad a job we did securing everything else than a problem with software development.
If the argument was, "But my users all have perfectly nice long term private keys for some other system" then we could leverage that to get keys to make GitHub work, but in reality that's not the case. SSH keys are likely the most common private key† full stop even though they're only needed to do the 21st century equivalent of telnet
† For people anyway, for machines Let's Encrypt means there are an eye-watering number of new private keys minted each day by Certbot and similar tools.
"Pick a huge random number, this is a private key, you must never tell anybody else this key" is a fundamental operation. If they've never done this operation, that's more telling us how bad a job we did securing everything else than a problem with software development.
If the argument was, "But my users all have perfectly nice long term private keys for some other system" then we could leverage that to get keys to make GitHub work, but in reality that's not the case. SSH keys are likely the most common private key† full stop even though they're only needed to do the 21st century equivalent of telnet
† For people anyway, for machines Let's Encrypt means there are an eye-watering number of new private keys minted each day by Certbot and similar tools.