Optional metric handler for 'items' stats

        key: "items:<slab_id>:<metric_name>" format
        value: return untouched

        Like all optional metric handlers returns metric, tags, value

def get_items_stats(key, value):
        """
        Optional metric handler for 'items' stats

        key: "items:<slab_id>:<metric_name>" format
        value: return untouched

        Like all optional metric handlers returns metric, tags, value
        """
        itemized_key = key.split(':')
        slab_id = itemized_key[1]
        metric = itemized_key[2]

        tags = ["slab:{}".format(slab_id)]

        return metric, tags, value