Histogram aggregation supports an 'offset' option to move bucket boundaries.
In a histogram with buckets of size X these can be moved from 0, X, 2X, 3X,...
by an offset value of Y to Y, X+Y, 2X+Y, 3X+Y... by using the 'offset' option.
The previous 'pre_offset' and 'post_offset' options are removed in favour of
the simplified 'offset' option.
Closes#9417Closes#9505