Add possibility that a output of multiple tasks become input for a task

[alifbe]

One example use case, we can have multiple tasks (could be different type) that produce RegularSurface object. We also have a task that take List[Surface] as input.

graph LR
    A[Load surface] -- "Surface A" --> J[ ]
    B[Generate surface] -- "Surface B" --> J
    C[Generate surface] -- "Surface C" --> J
    D[Load surface] -- "Surface D" --> J
    J -- "List[Surface]" --> Main[Create Grid]

    style J width:0px,height:0px,stroke:none 

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