add aten.sum.dim_IntList (#2796)

Summary:
Pull Request resolved: https://github.com/pytorch/executorch/pull/2796

` aten.sum.dim_IntList` reads in a parameter `dims` which are the dimensions we want to reduce. We process these dimensions one by one by adding intermediate nodes to store the intermediate output.

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Reviewed By: jorgep31415

Differential Revision: D55288560

fbshipit-source-id: e46e7f686aa61f27d38cf7fa9b20af853704d1cd