Avoid deprecation with interval for DateHistogram

[VincentLanglet]

This could be a way to solve #2097

[franmomu]

what about creating setCalendarInterval, setFixedInterval and deprecate setInterval? to be in sync with elasticsearch

[VincentLanglet]

what about creating setCalendarInterval, setFixedInterval and deprecate setInterval? to be in sync with elasticsearch

DateHistogram extends Histogram, and the Histogram constructor expects a interval value as third parameter (and then call setInterval in the constructor).
I thought about adding a 4th parameter to set if it's calendar or fixed, but this can automatically be determined like I did, so it's kinda useless.
Also, the setInterval method is coming from the Histogram class. So if you want to remove it, you need to stop extending Histogram.

An other strategy started in #1874 but never ended...

[thePanz]

I like this approach, later we could deprecate the setInterval.

We should also add the setCalendarInterval and setFixedInterval methods as suggested by @franmomu, to allow users to properly set the intervals following the ES documentation.

WDYT?

Later we could even have 2 different classes implementing the CalendarIntervaDateHistograml and FixedIntervalDateHistogram, so that we could enforce the creation of valid objects.
This would be a topic for another PR, imho.

[VincentLanglet]

I like this approach, later we could deprecate the setInterval.

We should also add the setCalendarInterval and setFixedInterval methods as suggested by @franmomu, to allow users to properly set the intervals following the ES documentation.

WDYT?

Done @thePanz

[thePanz]

LGTM, thanks @VincentLanglet!
Would you add the changes to the Changelog?

[thePanz]

Merged in d4849e2
Thanks @VincentLanglet !