secrets: always add Content-Length header
    
    If custodia server does not reply with Content-Length header, curl may
    wait for non-existing body of http reply if such body does not exist
    (for example during POST operation when creating a container).
    
    Reviewed-by: Simo Sorce <simo@redhat.com>
    Reviewed-by: Jakub Hrozek <jhrozek@redhat.com>