[Gym] Setup tutorial contains instructions that should be moved to container build stage

[jbaczek]

Is your feature request related to a problem? Please describe.
The setup guide contains instructions to install things that should already be present in the release container.

1. All the code needed to run tutorial should be present in a release container. This section shouldn't be necessary:

# Clone NeMo RL repository
git clone https://github.com/NVIDIA-NeMo/RL
cd RL

# Initialize all submodules (Gym, Megatron, AutoModel, etc.)
git submodule update --init --recursive

2. Docker already serves a purpose of isolated environment. Using venv inside a container defies the purpose of dockerization.

# Setup Gym local venv
cd 3rdparty/Gym-workspace/Gym
uv venv --python 3.12 --allow-existing .venv
source .venv/bin/activate
uv sync --active --extra dev

Describe the solution you'd like

The example workloads should be runnable with way easier setup. No installing stuff in runtime!

Describe alternatives you've considered
N/A

Additional context
This requests comes from my attempts to go through the setup guide and single node tutorial. These steps are adding unnecessary overhead to the process