Deprecate adGroupDetails.childAdType in favor of adDetails.adType on individual ads

[ejsuncy]

Problem

xdm:childAdType on adGroupDetails is redundant and inaccurate:

1. Redundant: adDetails.adType already exists on each individual ad in the Ad Lookup schema with a full enum of 35+ values.
2. Inaccurate: childAdType is a single string — it cannot represent ad groups that contain mixed ad types (common on Meta, TikTok, and other platforms). Setting it for heterogeneous groups requires leaving it blank or using "other", making the field useless.

Solution

Soft-deprecate xdm:childAdType by:

• Updating the description to indicate it is deprecated and point consumers to adDetails.adType
• Adding "meta:status": "deprecated"

Impact

Consumers should use adDetails.adType on each ad record in the Ad Lookup to determine ad type, which handles mixed-type ad groups correctly.