Absolute action + two arm env fix

[Abhiram824]

What this does

Fixes #737

It specifically fixes two issues when initializing two robots.

1. Reference poses in WHOLE_BODY_IK were incorrect for the second robot in any TwoArmEnv
2. With absolute action control, the pose of the robot not being controlled is not maintained

How it was tested

Run any environment with two robots with absolute action control before and after these changes were made for example

python robosuite/scripts/collect_human_demonstrations.py --environment TwoArmLift --device spacemouse --robots Panda Panda --config parallel --controller WHOLE_BODY_IK

Before the changes the second robot will never stay in the same pose when not being controller After these changes they do

[kevin-thankyou-lin]

we do need the same change for whole_body_mink_ik.json? would things work if we directly set gripper0_ instead of gripper{idx}?

[Abhiram824]

we do need the same change for whole_body_mink_ik.json? would things work if we directly set gripper0_ instead of gripper{idx}?

good point, ill update mink as well