Add support for summarize and nonNegativeDerivative

[criemen]

Hello,
I've counters in my metrics, like total numbers of search executed.
When I want to graph these as search rate per minute, derivative() oder derivative => true in the DSL doesn't work, but I need summarize(nonNegativeDerivative(series, '1min')) for the outcome to be correct.
It would be nice to get this in the DSL, both nonNegativeDerivative instead of derivative and summarize added to the call.
The other use case which should be kept in mind is that when I compute the search rate per minute over the whole cluster, i use the call
summarize(sumSeries(nonNegativeDerivative((*.mysearchcount)), '1min')
which still should be supported, if not integrated into the DSL syntax.
Thanks for considering my feature request

[davewongillies]

nonNegativeDerivate is already supported by the :non_negative_derivative option. summarize isn't currently though. It'd definitely be a handy option to have. I'll look into adding it to the DSL.