What should we add?

Since #14006 merged we now have a representation of a circuit in the C API. However in that PR one component we didn't include was the function to add a UnitaryGate to the circuit. We can take a pointer to an array from the C caller and pass that to ndarray to create a UnitaryGate object. Right now UnitaryGate only supports an owned array type ArrayType::NDArray this could be extended to store an ArrayView2 and leave the array in the caller managed memory, but doing this would have implications for lifetime tracking in the circuit so it might not be worth it. Considering we return a copy of the array when Operation::matrix() is called, the overhead of copying the array once from the C caller into what we put on the circuit doesn't seem like the worst tradeoff.