[HUMANOID] Stand up policy

[DarinAnthony]

Feature Overview
Create a policy to get the humanoid robot to stand up.

Describe the solution you'd like
Use IsaacSim/MuJoCo to train the RL policy to stand the humanoid robot from a position laying down. Perhaps try randomizing a bit further from different positions (seated, etc).

Steps to Implement
Use the same domain randomization seen in locomotion, but change up the rewards and environment initialization for standing up.

Testing
Train in one sim, validate in another, then deploy to the real robot.

[DarinAnthony]

Things to change include:

ROBOT SIDE:

1. New URDF/XML for full humanoid robot with arms
2. Tune the motors

ENVIRONMENT SIDE:

1. Using baselines tritonhumanoid_env.py and tritonhumanoid_env_cfg.py, change the restart conditions (initial position of robot) to be in fallen positions
2. Either: Write your own rewards for standing up, or use MOCAP data as a reward to track