Suppress noisy Alembic plugin setup logs

[ephraimbuddy]

Alembic emits autogenerate plugin registration messages at INFO during CLI startup. Those unrelated lines contaminate machine-readable command output, while warnings and errors still need to remain visible.

closes: #69911

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GPT-5.6

[Copilot]

Pull request overview

This PR fixes CLI machine-readable output (e.g. --output json) being polluted by stdlib-logging output from dependencies (notably Alembic), by making [logging] namespace_levels apply consistently to both structlog and Python’s standard-library logging loggers. It also lowers the handler threshold when needed so per-namespace verbosity can be higher than the global level without being dropped.

Changes:

• Apply namespace_levels to stdlib loggers by setting per-logger levels after dictConfig, and adjust the default handler level to the most verbose configured level so overrides can take effect.
• Default alembic.runtime.plugins to WARNING to suppress noisy plugin-registration logs during normal CLI commands.
• Add regression tests for stdlib namespace filtering and the Alembic default; update config docs to reflect behavior and namespace hierarchy.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
shared/logging/src/airflow_shared/logging/structlog.py	Applies namespace levels to stdlib loggers, lowers handler threshold when required, and suppresses Alembic plugin logs by default.
shared/logging/tests/logging/test_structlog.py	Adds tests covering stdlib namespace filtering, allowing per-namespace verbosity below the global level, and the Alembic logger default.
airflow-core/src/airflow/config_templates/config.yml	Documents that namespace_levels applies to both structlog and stdlib logging and clarifies hierarchical namespace behavior.

[amoghrajesh]

logging.getLogger(logger_name).setLevel(level) sets a stdlib logger level directly on the global logger object, outside dictConfig. Once set, it stays set on that logger for the rest of the process & a later configure_logging() call that does not mention that same logger name will not reset it back. Seems like a quirk we should be aware about or handle in dictConfig?

[ashb]

I was 90% sure the namespace logging working for stdlib logging already without needing this change? Did I make that up

[ephraimbuddy]

I have refocused this PR to just silence the chatty plugin.

The second issue I tried fixing can be seen when you run AIRFLOW__LOGGING__NAMESPACE_LEVELS=alembic.runtime.plugins=WARNING airflow dags list --columns dag_id,fileloc,owners,is_paused --output json in a branch not having this fix

[ashb]

Wrong fix IMO -- why is alembic being imported so early?