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Update the Franka Stacking Env to align with Robosuite stacking task
used in MimicGen.

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---------
Signed-off-by: peterd-NV <peterd@nvidia.com>
Co-authored-by: CY Chen <cyc@nvidia.com>
Co-authored-by: oahmednv <oahmed@Nvidia.com>
Co-authored-by: Toni-SM <aserranomuno@nvidia.com>