Add/restructure Media Analytics fields in XDM

## What are the schemas that are affected by the issue
* advertising-timed-asset-reference.schema.json
* advertising.schema.json
* media-timed-asset-reference.schema.json
* media-timed-audio.schema.json [NEW]
* media-timed-chapter.schema.json
* media-timed-qoe.schema.json
* media-timed.schema.json

## What are examples of products that are impacted by the issue
* Adobe Media Analytics

Internal JIRA issue: https://jira.corp.adobe.com/browse/VA-3365

High-level changes:
* addition of ad properites
* addition of video properties
* restructuring of audio fields to separate them from video fields
* move misplaced field (dropBeforeStart)

Review the listed advertising and media schema files, including the new media-timed-audio.schema.json, and compare their current field organization with the issue's high-level Media Analytics changes. Trace how ad, video, audio, and dropBeforeStart fields are represented across the schemas. Done means the affected schemas consistently include the additions and restructuring described in the issue.

Written by the indexing model from the issue text.