integrate method for Series and DataFrame

[scls19fr]

Hello,

Similar to #26680 when dealing with sensors data such as power meter or flow meter and having such data in a DataFrame (or in a Series) it can be convenient to easily calculate integral of values ie calculate energy consumption from power usage, volume consumption from flow rate for example.

Maybe Series and DataFrame could have an integrate method.

Similar question have been asked on StackOverflow

https://stackoverflow.com/questions/50239878/pandas-dataframe-column-numerical-integration

Maybe it could be worth to provide a better integration with Scipy and make use of scipy.integrate.trapz.

Kind regards

PS : related issue may be #3759

[jreback]

same rationale as here: #26680 (comment)

these are not core to pandas, but could be easily added via another package and hook into the accessor api.