Align Oracle/Spanner Histogram/Statistics implementations

DBZ-6899 introduced a new DurationHistorgramMetric that is responsible for tracking the min/max/last/total values of duration-based values used by Oracle.

There is somewhat of a similar concept in Spanner's Statistics class; however, there they have this concept of {{QuantileMeter]} that starts a thread per metric. We should coordinate this with nancyxu567@gmail.com to see how best we can align these so that they can be refactored into the core module and reused across connectors.