Changes to List avatars for talking-head videos

api operation id elements.listAvatars removed and replaced with listAvatars

added the non-success response with the status 409

added the non-success response with the status 404

added the non-success response with the status 400

added the non-success response with the status 503

the oneOf[subschema #1]/data response's property type changed from no type to object for status 403

the response property oneOf[subschema #1]/data became required for the status 403

added the required property oneOf[subschema #1]/data/feature to the response with the 403 status