Add sshd-auth binary for OpenSSH 10.0

https://www.openssh.com/releasenotes.html * sshd(8): this release removes the code responsible for the user authentication phase of the protocol from the per- connection sshd-session binary to a new sshd-auth binary. Splitting this code into a separate binary ensures that the crucial pre-authentication attack surface has an entirely disjoint address space from the code used for the rest of the connection. It also yields a small runtime memory saving as the authentication code will be unloaded after the authentication phase completes. This change should be largely invisible to users, though some log messages may now come from "sshd-auth" instead of "sshd-session". Downstream distributors of OpenSSH will need to package the sshd-auth binary.