Torch.RL: A2C & PPO

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Description

Kudos to https://github.com/lcswillems/rl-starter-files.

Related Issue

Checklist

• [ ] Have you run colab CI/CD with jax_dl requirements? Please attach the notebook link.
• [ ] Have you run colab CI/CD with keras_dl requirements? Please attach the notebook link.
• [ ] Have you run colab CI/CD with torch_dl requirements? Please attach the notebook link.
• [ ] Have you checked Jax XLA integration? Please attach the notebook link.
• [ ] Have you checked Torch XLA integration? Please attach the notebook link.