Add automatic update scan and notification for custom nodes on ComfyUI startup

## Feature Suggestion

Enhance ComfyUI-Manager by enabling it to automatically scan all installed custom nodes for available updates each time ComfyUI starts.

### Proposed workflow:
- On startup, ComfyUI-Manager checks installed custom nodes for updates.
- If any updates are found, notify the user in the UI.
- Provide a convenient option for the user to update nodes directly from the notification.

This feature will streamline node management, ensure users are running the latest versions, and improve overall usability.

**Benefits:**
- Reduces manual update checks
- Keeps custom nodes up-to-date
- Makes management more convenient