Get events usage

Get time-series arrays of the number of times a flag is evaluated, broken down by the variation that resulted from that evaluation. The granularity of the returned data depends on the length of the requested time range: ranges shorter than two hours return minutely data, ranges shorter than two days return hourly data, and ranges of two days or longer return daily data. Minutely data is retained for 70 days; a range shorter than two hours that starts before then is returned at hourly granularity instead, with the start of the range widened to the containing hour. Ranges that predate available data return an empty series list. If a flag has served many distinct variation values in the requested range, the least recently seen values may be aggregated into a single additional series labeled "Other Variations".