Migrate MaxText Docker images to Artifact Registry

[SurbhiJainUSC]

Description

• Migrate Maxtext Docker images from gcr.io to Artifact Registry (us-docker.pkg.dev) for MOSS Compliance

Tests

https://github.com/AI-Hypercomputer/maxtext/actions/runs/34637261590

Checklist

Before submitting this PR, please make sure (put X in square brackets):

• I have performed a self-review of my code. For an optional AI review, add the gemini-review label.
• I have necessary comments in my code, particularly in hard-to-understand areas.
• I have run end-to-end tests tests and provided workload links above if applicable.
• 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.

[gemini-code-assist]

Code Review

This pull request updates the documentation and usage instructions in both clean_py_env.Dockerfile and clean_py_env_gpu.Dockerfile. Specifically, it updates the Docker build, authentication, and push commands to reference the Google Artifact Registry (us-docker.pkg.dev) instead of the legacy Google Container Registry (gcr.io). I have no feedback to provide as there are no review comments and the changes are straightforward documentation updates.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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