[arm] New Arm Control

[KeseterG]

Description

This PR does the following:

• Added full MuJoCo model for Walli Arm V2
• Added QP-Based IK Controller for the arm
• Added twist_sender for easier testing

Testing Steps (if relevant)

Check README.md inside urc_arm_py.

Test Case 1

1. Launch mjsim.launch.py inside urc_arm_py.
2. Send a twist command to the arm with Foxglove.
3. See if the arm moves to the desired location, indicated by the red cube.

Test Case 2

1. Run twist_sender in a separate terminal.
2. Launch mjsim.launch.py inside urc_arm_py.
3. See if the arm moves to the desired location, indicated by the red cube, changed upon keyboard control.

Expectation: You should see the arm move in the MuJoCo simulation and the command output change inside the /qp_ctrl/pos_ctrl topic.

[yambati03]

One quick thing—I think this PR picked up a lot of unrelated changes. You might have to rebase against the latest version of master to fix.