'Polls the data from prometheus and pushes them as gauges
`endpoint` is the metrics endpoint to use to poll metrics from Prometheus
Note that if the instance has a \'tags\' attribute, it will be pushed
automatically as additionnal custom tags and added to the metrics'

def process(self, endpoint, send_histograms_buckets=True, instance=None):

    (content_type, data) = self.poll(endpoint)
    tags = []
    if (instance is not None):
        tags = instance.get('tags', [])
    for metric in self.parse_metric_family(data, content_type):
        self.process_metric(metric, send_histograms_buckets=send_histograms_buckets, custom_tags=tags, instance=instance)
