feat: variadic inputs

[jjangga0214]

Hi!

Sometimes variadic provides convenience.

For example, a custom node MultiAreaConditioning allows users to add 2 or more conditional inputs. If a user right-click, an option like 'insert input above' appears.

The developer Davemane42 enables this by custom js. https://github.com/Davemane42/ComfyUI_Dave_CustomNode/blob/main/javascript/MultiAreaConditioning.js

I think this behavior is very useful. So natively supporting variadic would be great.

How do you think?

Thank :)

[ltdrdata]

I also had the thought of having a scalable input. However, since that feature is specialized for that specific node, it requires careful consideration to make it more general.