We add new key exchange algorithms and new enums for PubkeyAuthOptions.
We also add new keywords from sshd_config.5 not present here and remove
keywords present here that are not present in the official
documentation, with the exception of those patched in by Debian and
Fedora, as well as ChallengeResponseAuthentication which is deprecated
but still functional.
closes: vim/vim#1934704c3c6871e
Co-authored-by: Fionn Fitzmaurice <fionn@github.com>