Don't use averages for grafana display

[hageboeck]

Graphs in grafana display results averaged over a few days. This waters down improvements/regressions. It would be great to see results jump to new values the day after a merge.

Example: graph at the bottom here: https://rootbnch-grafana-test.cern.ch/d/ENlOG7EWz/roofit-benchmarks-vectorized-pdfs?orgId=1

This difference should have been a ~ 2x speed up, but you just don't see that.

[eguiraud]

(note that only some graphs are affected, not all)