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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _create_gitlab_prometheus_instance(self, instance, init_config):
 """ Set up the gitlab instance so it can be used in OpenMetricsBaseCheck """

        # Mapping from Prometheus metrics names to Datadog ones
        # For now it's a 1:1 mapping
        allowed_metrics = init_config.get('allowed_metrics')
        if allowed_metrics is None:
            raise CheckException("At least one metric must be whitelisted in `allowed_metrics`.")

        gitlab_instance = deepcopy(instance)
        # gitlab uses 'prometheus_endpoint' and not 'prometheus_url', so we have to rename the key
        gitlab_instance['prometheus_url'] = instance.get('prometheus_endpoint')

        gitlab_instance.update(
            {
                'namespace': 'gitlab',
                'metrics': allowed_metrics,
                # Defaults that were set when gitlab was based on PrometheusCheck
                'send_monotonic_counter': instance.get('send_monotonic_counter', False),
                'health_service_check': instance.get('health_service_check', False),
            }
        )

        return gitlab_instance