feat: Support pre-training and post-training callbacks in promote_docker_image workflow

[RexBearIU]

Description

Update .github/workflows/promote_docker_image.yml to handle both pre-training and post-training GitHub repository dispatch callbacks (airflow-dag-complete) independently.

• Log TEST_TYPE (pre_training / post_training) from github.event.client_payload in the handle_result step.
• Update the tag_docker_image matrix strategy to match test_type to its corresponding target Docker image:
  • pre_training: promotes maxtext_jax_nightly and maxtext_gpu_jax_nightly.
  • post_training: promotes maxtext_post_training_nightly.
• Added a check (github.event.client_payload.test_type == '' || github.event.client_payload.test_type == matrix.test_type) so that each callback promotes only its relevant Docker images, while preserving full backward compatibility if test_type is omitted.

Tests

• Validated YAML syntax with yamllint .github/workflows/promote_docker_image.yml.
• Verified condition logic for test_type matrix evaluation (pre_training -> maxtext_jax_nightly, maxtext_gpu_jax_nightly; post_training -> maxtext_post_training_nightly; empty -> all images).

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.

[gemini-code-assist]

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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