Fix train_rl.py post restructure

[A9isha]

Description

Bring back some missing changes since the restructure

If the change fixes a bug or a Github issue, please include a link, e.g.,:
FIXES: b/486274740

Tests

Ran train_rl.py locally on a v5p-8

python3 -m src.maxtext.trainers.post_train.rl.train_rl src/maxtext/configs/post_train/rl.yml   model_name=llama3.1-8b   tokenizer_path=meta-llama/Llama-3.1-8B-
Instruct   load_parameters_path=/path/to/checkpoint   run_name=maz-8b-$RANDOM   base_output_directory=/path/to/gcs/location   hf_access_token=$HF_TOKEN dataset_name=gsm8k steps=4

Checklist

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• I have made or will make corresponding changes to the doc if needed, including adding new documentation pages to the relevant Table of Contents (toctree directive) as explained in our documentation.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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