Add documentation for changing authentication type of session.

It took a fair amount of digging to find that setting the "PreferredAuthentications" option for creating a session allows you to change the auth type. It was defaulting to Kerberos for me.

Scroll down to "User Authentication Methods" for all of the options.
https://epaul.github.io/jsch-documentation/javadoc/com/jcraft/jsch/JSch.html#setConfig-java.lang.String-java.lang.String-

Start with the linked JSch Javadoc and read the “User Authentication Methods” section, focusing on the PreferredAuthentications option used when creating a session. Add documentation explaining how to change the authentication type and list the available options; the payload does not identify the repository file or documentation entry point.

Written by the indexing model from the issue text.