Introduce REST API for event broadcasting

[devleejb]

Description:
The recent addition of the event Broadcast functionality in the yorkie-js-sdk (referenced in this PR) has been a great enhancement. However, currently, this feature is only accessible through the yorkie-js-sdk. It would be beneficial to extend this functionality to allow for event broadcasting through a REST API.

For reference, LiveBlocks provides a REST API for broadcasting events, as detailed here. I propose implementing a similar REST API endpoint in Yorkie.

Why:
Introducing a REST API for event broadcasting will enhance flexibility and enable broader usage scenarios, allowing users who prefer RESTful interactions to leverage the event functionality without being limited to the SDK. This would cater to a wider audience and potentially increase adoption of the feature.