Change Listeners/Event Notifications for DA content

To ensure features like Search remains consistent and up-to-date, we need to implement change listeners for the content. These listeners will monitor changes in the underlying content and notify the Search system to make necessary updates to indexed documents. Basic change events are needed to support this feature, like :
1. file created
2. file moved
3. file deleted
4. file modified

There could be a periodic post of the change log similar to journaling APIs , or a way to register client application's own webhook to receive these events.

Start by mapping where DA content changes are handled and how the Search system currently receives updates. Clarify whether the change log or client webhooks is the delivery mechanism, define the four required events, and consider the work complete when each event can notify Search reliably.

Written by the indexing model from the issue text.