* Add support for ed25519_sk and ecdsa_sk SSH keys
These start with sk-ssh-ed25519@openssh.com and sk-ecdsa-sha2-nistp256@openssh.com.
They are supported in recent versions of go x/crypto/ssh and OpenSSH 8.2
or higher.
* skip ssh-keygen
Signed-off-by: Andrew Thornton <art27@cantab.net>
Co-authored-by: Andrew Thornton <art27@cantab.net>