[Issue #1818] Mark descriptorTimeSeriesGranularity as stable and add optional timezone property

[clubycoder]

This is for issue #1818

The timezone was added the same way as Place Context that is used in Experience Events:

xdm/components/datatypes/placecontext.schema.json

Line 25 in 43bf2a1

"xdm:ianaTimezone": {

[anandphatak]

Change looks good. Do you want to consider updating the example file? https://github.com/adobe/xdm/blob/master/schemas/descriptors/time-series/descriptorTimeSeriesGranularity.example.1.json

[clubycoder]

Change looks good. Do you want to consider updating the example file? https://github.com/adobe/xdm/blob/master/schemas/descriptors/time-series/descriptorTimeSeriesGranularity.example.1.json

Good call...added.