Addition of Summary Metrics class

[clubycoder]

What are the schemas that are affected by the issue

New Summary Metrics schema - https://ns.adobe.com/xdm/context/summarymetrics - extending the existing time-series behavior along with a new descriptor - https://ns.adobe.com/xdm/descriptors/descriptorTimeSeriesGranularity - that provides the specifics for the granularity of the summary.

What are examples of products that are impacted by the issue

This class will be used for Adobe Customer Journey Analytics, Adobe Intelligent Services, Adobe Experience Platform ingestion of summary metrics, and additional future Adobe products dealing with summary data vs raw events.