pages/yubikey: rework the local auth section
    
    Changed the structure and content of the section to reflect more modern
    tooling available in recent Fedora Linux distributions.
    
    Simplified overall structure and added challenge-response configuration.
    
    Removed the more complicated authfile option as it is an option for more
    advanced use-cases but not necessary for a basic setup. More advanced
    users may refer to the pam_yubico man page.
    
    Added a warning about locking yourself out when using required
    configuration.