Task to implement proposal found in T344751#9247383

In T344751#9175304, @Krinkle wrote:

The handful of timing metrics we have (and actively make use of) vary a lot in their range. I'm not sure a single set can be of much use. The size and range of timing measures vary a lot throughout the platform, from job measures in the range between whole seconds and hours, to WANCache callbacks that are measures between 0.1 and 100 milliseconds.

To handle cases where a custom range of histogram buckets are needed, there should be a metric type that generates histograms based on a hardcoded set of buckets.

This task is complete when MediaWiki StatsLib can produce histograms in a set of counters following guidance provided by the Prometheus team.