[Feature Request] ComfyAPI Progress Status Messages for Custom Frontends

**Problem Description**
ComfyAPI is the best way to create API-based workflows for SD. In creating more complex workflows that take time for inference, keeping the user updated on status is becoming vital.

**Proposed Feature**
Allow the API to report the active node in a running workflow via messages / websockets (socket.io) / to allow the front-end to create a responsive progress indicator (e.g. Now Splitting Frames, Now Generating, Now Swapping Face...)