Add the PreferredAuthentications configuration to the SSH implementation with JSch

Current Situation

• The SOSVfsSFtpJCraft class uses the configured auth_method.

Desired Behavior

• The SOSVfsSFtpJCraft class makes sure, that no other authentication methods are allowed as a fallback by configuring the PreferredAuthentications-option with the auth_method only.
• Example: session.setConfig("PreferredAuthentications", options.auth_method)
• This should also be applied for JADE with the SFTP protocol for the source-, jump host- and target-settings.

Maintainer Notes

• This feature request has been reported by https://sourceforge.net/p/sosftp/feature-requests/2/