Provide DocEvent Webhook

[hackerwins]

What would you like to be added:

We are currently implementing an LLM-based document search functionality in CodePair. As part of this, we need to maintain a vector of document content in Vector Store. It's crucial that any updates to the document are reflected in the Vector Store by continually editing the content.

To achieve this, we require a mechanism that notifies external services like CodePair when documents are modified in Yorkie. We propose the introduction of a Webhook system that triggers when a document event occurs.

Specifically, we suggest that when handling the PushPullChanges requests, the server should check if a Webhook for the DocEvent is registered for the project. If it is, the server would call that Webhook during the background routine of the PushPullChanges API execution, right before publishing the DocEvent.

I think it will have a similar structure to the Auth Webhook, and if changes occur frequently, an event control device such as debouncing will also be needed.

Why is this needed:

This enhancement would enable seamless integration with external services, allowing for real-time updates to Search Engine or Vector Store based on document changes in Yorkie, thereby enhancing the overall document management and search capabilities of our application.