Fix config resolution for pip installed maxtext

[dipannita08]

Description

When we run maxtext workload with pip-installed maxtext, the config path does not get resolved correctly resulting in the need to clone MaxText to pass config when running with pip.

The resolve_config_path now handles this case, by resolving the config file using MAXTEXT_CONFIGS_DIR.

The rest of the description includes relevant details and context, examples:

• why is this change being made,
• the problem being solved and any relevant context,
• why this is a good solution,
• some information about the specific implementation,
• shortcomings of the solution and possible future improvements.

If the change fixes a bug or a Github issue, please include a link, e.g.,:
FIXES: b/491156065

Tests

• CI
• Build a test wheel and install in a tmp dir with no src/ folder:

uv pip install --python ~/maxtext/maxtext_venv_2/bin/python \
  "$(ls ~/maxtext/dist/maxtext-*.whl)[tpu]"
Using Python 3.12.13 environment at: /home/dishaw_google_com/maxtext/maxtext_venv_2
Resolved 263 packages in 783ms
      Built pylatexenc==2.10
Prepared 139 packages in 30.81s
Installed 262 packages in 1.23s

/tmp/maxtext_test$ ~/maxtext/maxtext_venv_2/bin/python3 -m maxtext.trainers.pre_train.train src/maxtext/configs/base.yml \
  run_name=dishaw_test_pip_install \
  base_output_directory=$OUTPUT_PATH \
  dataset_type=synthetic \
  steps=3

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.

[richjames0]

lgtm

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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[bvandermoon]

Awesome, thank you @dipannita08