certmonger: move 'criteria' description to module docstring
    
    The 'criteria' parameter is used by several subroutines in the
    ipalib.install.certmonger module.  It has incomplete documentation
    spread across several of these subroutines.  Move the documentation
    to the module docstring and reference it where appropriate.
    
    Part of: https://pagure.io/freeipa/issue/8186
    
    Reviewed-By: Rob Crittenden <rcritten@redhat.com>
    Reviewed-By: Rob Crittenden <rcritten@redhat.com>