[core] Graph begining by a residual are hard to express with Aidge

I wanted to create a MetaOperator for the swish operator:

swish(x)={{x}\over{1+e^{-\beta x}}}

This will translate to the following graph:

graph TD
    Input --> Div
    Input --> Mul --> Pow --> Add --> Div
    Beta("-Beta") --> Mul
    e --> Pow
    one("1") --> Add

However, doing this is not trivial as the graph view has to know that it has one Input and not two (the Input node for Mul and Div are the same).

Maybe we will need an identity node to represent this ?