Allow Queuing up Multiple Downloads at Once

### Checklist

- [ ] This feature I'm requesting is already implemented in yt-dlp.
- [ ] This feature is merely a UI/UX update.
- [x] This feature is suitable for primary users with little knowledge about yt-dlp.
- [ ] This feature is available for most websites, not only the video platform I use.
- [x] This feature is suitable for a large variety of videos.
- [x] This feature is not going to conflict with many of the existing options.

### Is your feature request related to a problem? Please describe.

_No response_

### Describe the solution you'd like

Let us queue up multiple downloads at a time

### Video link

_No response_

### Additional context

If you try to queue up another download, whilst one is already running, you get an error complaining something is already being downloaded