[Feature Request] Add Parametrizable InfluxQLNode Functions for Templating

I would like add as parameter in the template parameter file the InfluxQL funcion to apply over a certaing windows time.

This is what I can do now.

````javascript

var Period=1m
var Every=1m
var Field = 'value'

stream
|window()
.period(Period)
.every(Every)
|sum(Field)
`````

this is what I would like to do, at least for certain basic statistics like :

• Last: Select the last point.
• Max: Select the maximum point.
• Mean: Compute the mean of the data.
• Median: Compute the median of the data
• Min: Select the minimum point.
• MovingAverage: Compute a moving average of the last window points. No points are emitted until the window is full. Parametro extra: num de puntos
• Percentile: Select a point at the given percentile. Parámetro Extra: percentil
• Spread: Compute the difference between min and max points.
• Stddev: Compute the standard deviation.
• Sum: Compute the sum of all values.

````javascript

var Period=1m
var Every=1m
var Field = 'value'
var Func = 'sum'
stream
|window()
.period(Period)
.every(Every)
|InfluxEval(Func,Field)
`````
or

````javascript

var Period=1m
var Every=1m
var Field = 'value'
var Func = 'sum'
stream
|window()
.period(Period)
.every(Every)
|$Func(Field)
`````

Or something equivalent:

There is any plans to implement this new feature?

Thank you very much!

Review the template parameter file and the existing window()/sum() examples in the issue, then compare the proposed InfluxEval(Func, Field) and $Func(Field) entry points. Done means the supported basic statistics and any extra parameters are defined and usable through the chosen templating form, with behavior checked against the listed examples.

Written by the indexing model from the issue text.