Is your feature request related to a problem? Please describe.
Currently a series title is calculated from the series id prop. But it is not really useful, because series could have same labels in different series. In such case I currently can't create different series with same labels.

Describe the solution you'd like
It would be better to support to separate prop for a title (or label ):
<Series id={getSpecId(series.id + series.label)} title={series.label} />

or <Series id={getSpecId(series.id + series.label)} label={series.label} />

Additional context
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Kibana Cross Issues
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Checklist

• this request is checked against already exist requests
• every related Kibana issue is listed under Kibana Cross Issues list
• kibana cross issue tag is associated to the issue if any kibana cross issue is present