[Feature Request]: Loading spinner when uploading media to server

### Is there an existing issue for this?

- [x] I have searched the existing issues and checked the recent builds/commits

### What would your feature do ?

Currently when uploading item to remote, there is no indicator that uploading is in progress, which can be very annoying when ComfyUI is deployed on remote + slow connection.

### Proposed workflow

- Click upload
- Pick an image to upload
- Upload button on `LoadImage` node is disabled and show a spinner
- After upload completes, the spinner disappear and the upload button is active again

### Additional information

_No response_

┆Issue is synchronized with this [Notion page](https://www.notion.so/Issue-4012-Feature-Request-Loading-spinner-when-uploading-media-to-server-2016d73d365081878191d84a034550f4) by [Unito](https://www.unito.io)