Add gemma4-26b E2E test scripts for pre-training

[chiajunglien]

Description

This PR introduces end-to-end (E2E) testing and validation pipelines for the Gemma 4 26B model in MaxText.
Blocked by: https://buganizer.corp.google.com/issues/527749229

Tests

Pre-Training:

export RUN_ID=$(date +%Y-%m-%d-%H-%M)
bash tests/end_to_end/tpu/gemma4/26b/test_gemma4_to_mt.sh $RUN_ID
bash tests/end_to_end/tpu/gemma4/26b/test_gemma4.sh $RUN_ID

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.