[STORM-3565] add support for adding dimensions to metric data points

[RuiLi8080]

A dimensional metric collects information into multiple sub-categories (dimensions). Add an interface IDimensionalMetric extending IMetric in hope for supporting a better fine-grained metric reporting. DimensionalCountMetric serves as an example for creating and using dimensional metric

[kishorvpatil]

Having DimensionalCountMetric is excluding all other IMetric implementations that would required Dimensional implementation.

[RuiLi8080]

Re-worked on this PR. My thinking is to add a dimensions field in IMetricConsumer.DataPoint as an additional K-V metadata map. Data points are collected from metric measurement. The optional additional information could be helpful when downstream monitoring system want to organize or group those datapoints.