Add EnvironmentLogger Callback

[josejg]

This is a new callback to simplify logging environment metadata for reproducibility purposes:

• Git Commits for packages under workspace_dir, useful for mcli integrations
• Package versions for core dependencies, e.g. transformers
• Nvidia versions, including cuda, cuddn and nccl
• Docker image and tag
• Distributed info
• System info
• Gpu info

Main change is that GitPython now becomes a dependency. It is already a composer[dev] dependency. I was not sure if it was worth gating under a additional dependency