Feature Request: Add notification for item metadata change.

I was wondering if a webhook option could be added where a notification is generated when a media item's metadata is altered (like adding/removing a tag).

No files, tests, or entry points are identified. Start by locating how webhook notifications are generated and how media-item metadata changes are handled. Done means a metadata alteration, such as adding or removing a tag, generates the requested webhook notification.

Written by the indexing model from the issue text.