ssh: update to OpenSSH 9.1p1

Release notes are available at https://www.openssh.com/txt/release-9.1

9.1 contains fixes for three minor memory safety problems; these have
lready been merged to the copy of OpenSSH 9.0 that is in the FreeBSD base
system.

Some highlights copied from the release notes:

Potentially-incompatible changes

• ssh(1), sshd(8): SetEnv directives in ssh_config and sshd_config are now first-match-wins to match other directives. Previously if an environment variable was multiply specified the last set value would have been used. bz3438
• ssh-keygen(8): ssh-keygen -A (generate all default host key types) will no longer generate DSA keys, as these are insecure and have not been used by default for some years.

New features

• ssh(1), sshd(8): add a RequiredRSASize directive to set a minimum RSA key length. Keys below this length will be ignored for user authentication and for host authentication in sshd(8).
• sftp-server(8): add a "users-groups-by-id@openssh.com" extension request that allows the client to obtain user/group names that correspond to a set of uids/gids.
• sftp(1): use "users-groups-by-id@openssh.com" sftp-server extension (when available) to fill in user/group names for directory listings.
• sftp-server(8): support the "home-directory" extension request defined in draft-ietf-secsh-filexfer-extensions-00. This overlaps a bit with the existing "expand-path@openssh.com", but some other clients support it.
• ssh-keygen(1), sshd(8): allow certificate validity intervals, sshsig verification times and authorized_keys expiry-time options to accept dates in the UTC time zone in addition to the default of interpreting them in the system time zone. YYYYMMDD and YYMMDDHHMM[SS] dates/times will be interpreted as UTC if suffixed with a 'Z' character.
  
  Also allow certificate validity intervals to be specified in raw seconds-since-epoch as hex value, e.g. -V 0x1234:0x4567890. This is intended for use by regress tests and other tools that call ssh-keygen as part of a CA workflow. bz3468
• sftp(1): allow arguments to the sftp -D option, e.g. sftp -D "/usr/libexec/sftp-server -el debug3"
• ssh-keygen(1): allow the existing -U (use agent) flag to work with "-Y sign" operations, where it will be interpreted to require that the private keys is hosted in an agent; bz3429

MFC after: 2 weeks
Relnotes: Yes
Sponsored by: The FreeBSD Foundation

(cherry picked from commit 38a52bd3b5cac3da6f7f6eef3dd050e6aa08ebb3)
(cherry picked from commit ac5c465b9fdff74d1a73f63d157820887ff1787f)