updated image; added support for adding custom xla/libtpu flags

[ranuka123]

Description

This change updates maxtest.sh to use the correct Docker image, since running it will fail due to permission errors. It also adds timeout flags.

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Tests

Tested by running it locally on a v6e-256 pod.

Checklist

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• [X ] I have performed a self-review of my code. For an optional AI review, add the gemini-review label.
• [X ] 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.