Run several aggregation functions on the same database field in metric 1D

• In the current implementation, an internal error is raise when runnig a metric 1D using the column min(history.data.age) and mean(history.data.age) at the same time.
• It is is related to the use of the same database field with two different aggregation functions.
• It might be interesting to remove this bottleneck.
• One user case can be found in track_lhcbfrance metric1D / promotion per grade. The idea is to display at the same time the min, mean and max age for a given grade.