Concurrency running workflow

### Feature Idea

Run one workflow at same time
I.e. running with just diffrent prompt.
Of course in default should stay to run one at time, but in config it will be nice to increase.

This will also help with API calling

### Existing Solutions

Of corse we can run multiple instance of ComfyUI, but it will be waste of VRAM usage.

### Other

Maybe it can be done via custom-node?