Bug 3198

According to PROTOCOL.certkeys critical options must be lexically ordered by name:

```
Options must be lexically ordered by "name" if they appear in the
sequence. Each named option may only appear once in a certificate.
```

This works for the well-known options 'source-address' and 'force-command' but if custom critical options are passed, they will appear in the order passed in:

```
$ ssh-keygen -I key-id -O critical:a@foo.com=a -O critical:c@foo.com=c -O critical:b@foo.com=b -s ca.key user.pub
Signed user key user-cert.pub: id "key-id" serial 0 valid forever
```

They will be stored in the same order and will appear in that order when inspecting the certificate:
```
user-cert.pub:
        Type: ssh-rsa-cert-v01@openssh.com user certificate
        Public key: RSA-CERT SHA256:5XSDsn5usZ40pRyDsJnR2KWKacRc29ufR+U8KLYBqGw
        Signing CA: ECDSA SHA256:rmAjupXaId7QQode/ThbhY/t427k9EKtTfNQHn5AkPk (using ecdsa-sha2-nistp256)
        Key ID: "key-id"
        Serial: 0
        Valid: forever
        Principals: (none)
        Critical Options:
                a@foo.com UNKNOWN OPTION (len 5)
                c@foo.com UNKNOWN OPTION (len 5)
                b@foo.com UNKNOWN OPTION (len 5)
        Extensions:
                permit-X11-forwarding
                permit-agent-forwarding
                permit-port-forwarding
                permit-pty
                permit-user-rc
```