Keep provider_config_fallback_defaults.cfg in sync with provider.yaml

[FrankYang0529]

Why

• airflow-core/src/airflow/config_templates/provider_config_fallback_defaults.cfg is a hand-copied subset of provider config defaults. Core needs it while provider modules are being imported, before provider metadata is loaded. Nothing checks it against provider.yaml. Every entry in it is merged into configuration_description, so a stale entry keeps showing up in airflow config list.
• [atlas]: Remove atlas config #32776 removed the section from core config.
• [celery] worker_precheck: Disable ORM access from Tasks, DAG processing and Triggers #47320 removed it from the celery provider.
• [kubernetes_executor] worker_pods_queued_check_interval: Allow internal retries when pending k8s pod is deleted #45184 removed it from the cncf.kubernetes provider.
• [elasticsearch_configs] use_ssl: Upgrade Elasticsearch to 8 #33135 replaced use_ssl with http_compress.

How

• Remove the [atlas] section, worker_precheck and worker_pods_queued_check_interval; replace use_ssl with http_compress = False in [elasticsearch_configs].
• Drop the two docs lines that list password in [atlas] as _cmd / _secret capable.
• Replace the worker_precheck row in CFG_FALLBACK_CONFIG_OPTIONS (devel-common test data) with worker_prefetch_multiplier.
• Add the check-provider-config-fallback-defaults prek hook : every (section, option) in the cfg must be declared in some providers/**/provider.yaml with the same default. It runs whenever the cfg or a provider.yaml changes, and only checks that the cfg is a subset of provider.yaml.

Verification

• uv run --project scripts pytest scripts/tests/ci/prek/test_check_provider_config_fallback_defaults.py
• uv run --no-sync pytest airflow-core/tests/unit/core/test_configuration.py
• cd task-sdk && uv run --no-sync pytest tests/task_sdk/test_configuration.py

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Was generative AI tooling used to co-author this PR?

• Yes - Claude Code

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