OpenSSH certificate-based authentication and host verification

[gansheer]

Ref #8534

• Add test on OpenSSH certificate-based authentication and host verification for ftp and mina-sftp
• Use dynamically generated certs instead of repo files
• Use openssh-server container image instead of sshd-server (I found some limitations on certificates verification)

Notes:

• requires some refactoring
• a part of it will be backported on 3.33.x