Add the countDist aggregation to the stats, facet and timeseries Streaming Expressions

The unique function in the JSON facet API is currently not supported in the Streaming Expression pushdown analytics functions. This ticket will add support for unique aggregations in the stats, facet and timeseries Streaming Expressions. The name countDist will be the aggregation in Streaming Expressions and map to the JSON facet unique function.

Sample syntax:

facet(test, buckets="core_s", rows="50", countDist(type_s))