ability allow only 1 unique asset id in an input

[blanchco]

Description

• Adding a unique flag to the inputs so that we can check if we can add multiple of that value to the target port.
• Allows us to only connect unique model configs (or any other asset ids) into target ports

Edit

• Now a user can define whether or not the inputs are unique at an operator level by using the uniqueInputs key

[YohannParis]

LGTM, but should the uniqueness of an input be managed byt the node directly, and we should not have to precise that on the emit add input port.