Ticket 51177 - on upgrade configuration handlers
    
    Bug Description: 389 to function in docker and other environments
    such as restore-from-backup, needs to be able to upgrade it's configuration
    on startup. This lets us ship-and-enable new features, upgrade plugins
    and more (similar to libglobs upgrades)
    
    Previously we had only basic machinery for this (IE make sure this
    entry exists like this) which would always write the content. This
    caused problems where plugins would re-enable on restart, or couldn't
    be removed.
    
    Fix Description: This adds an upgrade processor and an exists_or_add
    so that we can do stateful creates of entries, but without trampling
    user modifications IE disabling plugins.
    
    https://pagure.io/389-ds-base/issue/51177
    fixes: #51177
    
    Author: William Brown <william@blackhats.net.au>
    
    Review by: tbordaz, mreynolds (Thanks!)