Changes to Get delivery metrics

deleted the query request parameter range

removed the optional property points/items/time_bucket from the response with the 200 status

added the new optional query request parameter granularity

added the new optional query request parameter group_by

added the new optional query request parameter period_end_at

added the new optional query request parameter period_start_at

added the new optional query request parameter time_zone

added the non-success response with the status 400

added the non-success response with the status 422

added the non-success response with the status 500

added the required property points/items/period_start_at to the response with the 200 status

endpoint added