Mark descriptorTimeSeriesGranularity as stable and add timezone

## What are the schemas that are affected by the issue

The descriptorTimeSeriesGranularity descriptor that is used with the Summary Metrics Class.

## What are examples of products that are impacted by the issue

Ingestion of paid media data that is aligned to a tiemzone other than UTC.

Locate the descriptorTimeSeriesGranularity descriptor and the Summary Metrics Class schema, then inspect nearby descriptors for stability markings and timezone fields. The issue does not identify files or tests, so first determine the relevant schema entry points and how schema validation is run. Done means the descriptor is marked stable and the timezone requirement is represented for the affected paid-media use case.

Written by the indexing model from the issue text.