OTel metrics: support specifying histogram boundaries

[lmolkova]

Default boundaries are { 0, 5, 10, 25, 50, 75, 100, 250, 500, 750, 1000, 2500, 5000, 7500, 10000 }; but the standard unit for duration is seconds.

Users can change default boundaries or configure to use exponential ones, but users who didn't would have aa data in the second bucket and very skewed latency information.

We need to be able to configure explicit histograms for each metric on the metrics API.