Add/Update Metadata

Lets you update or append metadata for assets that have already been ingested. You can reference assets either by source_path or asset_id. If source_path is duplicated or was a presigned URL, using asset_id is strongly recommended to ensure accuracy. The `update_type` parameter controls how metadata updates are applied. By default, it is set to *`upsert`*, which *adds or updates* the provided metadata *without removing any existing entries*. To completely replace the existing metadata instead, set `update_type` to *`overwrite`* — this will *clear all current metadata and apply only the new values*.