Plugin InstantSSH: Added: Authentication options validator

    [feedquote='i-MSCP Github (plugins) (nuxwin)','https://github.com/i-MSCP/plugins/commit/9555c6b166741236d8d4701919c71672d8581485']

    Code
    1. Plugin InstantSSH: Added: Authentication options validator
    2. Plugin InstantSSH: Configuration option allowing to define which SSH authentication options can be overriden by customers
    3. Plugin InstantSSH: Fixed: Unable to update plugin in some contexts
    4. Plugin InstantSSH: Small fixes

    [/feedquote]