AggregationDataStore: Support Group By for Metric Columns

[aklish]

The AggregationDataStore needs to construct a custom JPQL query that aggregates over the requested metric columns, grouping by the requested dimension columns.

This ticket depends on issues #818, #819, #820, and #823.

Expected Behavior

The JPQL queries must continue to support:

1. Sorting
2. Pagination
3. Page Totals
4. Filters
5. Prefetching to-one relationships
6. Filter joins across to-one relationships

In addition, it must add:

1. Generating aggregation expression for MetricAggregation attributes.
2. Generating group by clauses for requested dimensions.
3. Generating metric expressions for ComputedMetric attributes.

Context

#804