In order to make the configuration more migratable between systems, the RPKI SSH authentication is yet not moved to the PKI subsystem.
Introduce OpenSSH key support
```
set pki openssh rpki private key ...
set pki openssh rpki public key ...
set pki openssh rpki public type 'ssh-rsa'
```
Example:
```
set pki openssh rpki private key 'b3BlbnNzaC1rZXktdjEAAAAABG5vbmUAAAAEbm9uZQAAAAAAAAABAAABFwAAAAdzc2gtcnNhAAAAAwEAAQAAAQEAweDyflDFR4qyEwETbJkZ2ZZc+sJNiDTvYpwGsWIkju49lJSxHe1xKf8FhwfyMu40Snt1yDlRmmmz4CsbLgbuZGMPvXG11e34+C0pSVUvpF6aqRTeLl1pDRK7Rnjgm3su+I8SRLQR4qbLG6VXWOFuVpwiqbExLaU0hFYTPNP+dArNpsWEEKsohk6pTXdhg3VzWp3vCMjl2JTshDa3lD7p2xISSAReEY0fnfEAmQzH4Z6DIwwGdFuMWoQIg+oFBM9ARrO2/FIjRsz6AecR/WeU72JEw4aJic1/cAJQA6PiQBHwkuo3Wll1tbpxeRZoB2NQG22ETyJLvhfTaooNLT9HpQAAA8joU5dM6FOXTAAAAAdzc2gtcnNhAAABAQDB4PJ+UMVHirITARNsmRnZllz6wk2INO9inAaxYiSO7j2UlLEd7XEp/wWHB/Iy7jRKe3XIOVGaabPgKxsuBu5kYw+9cbXV7fj4LSlJVS+kXpqpFN4uXWkNErtGeOCbey74jxJEtBHipssbpVdY4W5WnCKpsTEtpTSEVhM80/50Cs2mxYQQqyiGTqlNd2GDdXNane8IyOXYlOyENreUPunbEhJIBF4RjR+d8QCZDMfhnoMjDAZ0W4xahAiD6gUEz0BGs7b8UiNGzPoB5xH9Z5TvYkTDhomJzX9wAlADo+JAEfCS6jdaWXW1unF5FmgHY1AbbYRPIku+F9Nqig0tP0elAAAAAwEAAQAAAQACkDlUjzfUhtJs6uY5WNrdJB5NmHUS+HQzzxFNlhkapK6+wKqI1UNaRUtq6iF7J+gcFf7MK2nXS098BsXguWm8fQzPuemoDvHsQhiaJhyvpSqRUrvPTB/f8t/0AhQiKiJIWgfpTaIw53inAGwjujNNxNm2eafHTThhCYxOkRT7rsT6bnSio6yeqPy5QHg7IKFztp5FXDUyiOS3aX3SvzQcDUkMXALdvzX50t1XIk+X48Rgkq72dL4VpV2oMNDu3hM6FqBUplf9Mv3s51FNSma/cibCQoVufrIfoqYjkNTjIpYFUcq4zZ0/KvgXgzSsy9VN/4TtbalrOuu7X/SHJbvhAAAAgGPFsXgONYQvXxCnK1dIueozgaZg1I/n522E2ZCOXBW4dYJVyNpppwRreDzuFzTDEe061MpNHfScjVBJCCulivFYWscL6oaGsryDbFxO3QmB4I98UBqrds2yan9/JGc6EYe299yvaHy7Y64+NC0+fN8H2RAZ61T4w10JrCaJRyvzAAAAgQDvBfuV1U7o9k/fbU+U7W2UYnWblpOZAMfi1XQP6IJJeyWs90PdTdXh+l0eIQrCawIiRJytNfxMmbD4huwTf77fWiyCcPznmALQ7ex/yJ+W5Z0V4dPGF3h7o1uiS236JhQ7mfcliCkhp/1PIklBIMPcCp0zl+s9wMv2hX7w1Pah9QAAAIEAz6YgU9Xute+J+dBwoWxEQ+igR6KE55Um7O9AvSrqnCm9r7lSFsXC2ErYOxoDSJ3yIBEV0b4XAGn6tbbVIs3jS8BnLHxclAHQecOx1PGn7PKbnPW0oJRq/X9QCIEelKYvlykpayn7uZooTXqcDaPZxfPpmPdye8chVJvdygi7kPEAAAAMY3BvQExSMS53dWUzAQIDBAUGBw=='
set pki openssh rpki public key 'AAAAB3NzaC1yc2EAAAADAQABAAABAQDB4PJ+UMVHirITARNsmRnZllz6wk2INO9inAaxYiSO7j2UlLEd7XEp/wWHB/Iy7jRKe3XIOVGaabPgKxsuBu5kYw+9cbXV7fj4LSlJVS+kXpqpFN4uXWkNErtGeOCbey74jxJEtBHipssbpVdY4W5WnCKpsTEtpTSEVhM80/50Cs2mxYQQqyiGTqlNd2GDdXNane8IyOXYlOyENreUPunbEhJIBF4RjR+d8QCZDMfhnoMjDAZ0W4xahAiD6gUEz0BGs7b8UiNGzPoB5xH9Z5TvYkTDhomJzX9wAlADo+JAEfCS6jdaWXW1unF5FmgHY1AbbYRPIku+F9Nqig0tP0el'
```