Werk #7183: Metrics: Do not auto graph metrics that are part of a graph but have no metric_info

When adding a new metric to a service, the metric system automatically renders this metric as single graph until a graph definition is added that renders this metric. In this moment the automatically rendered metric is hidden.

This logic only worked for metrics that already have a metric_info definition. Now, if you add a new metric without specifying a metric_info for it, but add it to a graph_info, the automatically created single metric graph will now also be hidden.

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