Add `ReduceResolution` method to `Histogram` and `FloatHistogram`
This takes the original `mergeToSchema` function and turns it into a more generic `reduceResolution` function, which is the building block for the new methods.
The methods will help with addressing #12864.
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Signed-off-by: Ziqi Zhao <zhaoziqi9146@gmail.com>
The bucket receiving math.MaxFloat64 observations now has
math.MaxFloat64 as upper bound, while the bucket after it (the last
possible bucket) has +Inf.
This also adds a test for getBound and moves the getBound code to
generic.go (where it should have been in the first place).
Signed-off-by: beorn7 <beorn@grafana.com>