Add gripper to the Isaac simulation

[stevendes]

Summary

This patch adds the gripper to the AR4 Arm in Isaac. It also adds the necessary controllers for MoveIt to work.

Testing

Open the docker in ar4_isaac mode and build

./docker/run -s ar4_isaac
colcon build --packages-up-to ar4_isaac_bringup
source install/setup.bash

Run the simulation and move the ARM/Gripper

ros2 launch ar4_isaac_bringup main.launch.py

Note

When testing keep in mind the issue of MoveIt not executing consecutive moves, a workaround is to change planning groups before the next movement.

[stevendes]

@glpuga I added the refactor of the isaac_sim package here as well, PTAL

[IDavGal]

Looks good to me!
As discussed offline, the gripper planning group was failing to reach Open goals because of its definition in the moveit config file added in #24.

[stevendes]

Thanks @IDavGal ! I addressed the comment in the last commit.