anona-compute ssh

Open an OpenSSH session to a sandbox. anona-compute makes an ephemeral Ed25519 key
under $XDG_RUNTIME_DIR/anona-compute/ssh/<id>, has the gateway sign it (a 10-minute
certificate for the sandbox user), and runs the system ssh with
ProxyCommand "anona-compute ssh --proxy %n", which carries the connection over the
stream relay. Arguments after -- go to ssh (a remote command, -L, -R, ...).

--print-config prints an ssh_config block, so scp, rsync and editors can use
"Host <id>" directly; the certificate in it expires after 10 minutes, so run
it again (or anona-compute ssh) to renew.

anona-compute ssh SANDBOX_ID [-- SSH_ARGS...] [flags]