fix: update Megatron-DeepSpeed tutorial to match current repo structure (#7761)
docs: update Megatron-DeepSpeed tutorial to match current repo structure
- Update outdated file paths and script names in
`docs/_tutorials/megatron.md`.
- Replace `scripts/` with `examples/` for training scripts.
- Replace `pretrain_gpt2.py` with `pretrain_gpt.py`.
- Correct locations for `arguments.py` and `utils.py` to `megatron/`.
- Ensure tutorial instructions align with the latest Megatron-DeepSpeed
repository layout.
Resolves #7757
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Signed-off-by: leejianwoo-collab <leejianwoo@gmail.com>
Co-authored-by: Logan Adams <114770087+loadams@users.noreply.github.com>
Co-authored-by: Masahiro Tanaka <81312776+tohtana@users.noreply.github.com>