KCM: Configurable quotas for the secdb ccache back end
    
    Related:
    https://pagure.io/SSSD/sssd/issue/3386
    
    Exposes three new options for the [kcm] responder to set the global
    ccache limit, the per-uid ccache limit and the payload size.
    
    Reviewed-by: Michal Židek <mzidek@redhat.com>