Allows to pass in cols and rows as custom attributes for textareas in woocommerce_form_field()

Allows to pass in cols and rows as custom attributes for textareas in woocommerce_form_field(). 
You might want to set the size, especially the height, of a textarea with cols and rows rather than px or ems. I prefer to set the height with rows most times.

Example usage (changing rows and cols of order comments field on the checkout page):

    function custom_override_checkout_fields( $fields ) {
    
        $fields['order']['order_comments']['custom_attributes'] = array('cols' => 20, 'rows' => 9);

        return $fields;
    }
    add_filter( 'woocommerce_checkout_fields' , 'custom_override_checkout_fields' );