Add OpensearchRemoteLogIO.from_config and register opensearch scheme

[jason810496]

Part of #70265 (related: #67056).

Why

#67056 decoupled remote logging from the hardcoded branches in airflow_local_settings.py: core and
the Task SDK now resolve the handler via ProvidersManager dispatch on the
[logging] remote_base_log_folder URL scheme, instantiating the provider class through a no-arg
from_config() classmethod. This issue migrates the OpenSearch backend.

Design note (feedback welcome)

Unlike the object-storage backends, OpenSearch is currently selected by [opensearch] host being
set — remote_base_log_folder typically has no scheme for these deployments, so pure scheme
dispatch cannot reach it. The proposal (same as the sibling Elasticsearch issue #70271):

• Register an opensearch scheme and document setting
  [logging] remote_base_log_folder = opensearch:// as the forward-looking configuration.
• Keep the legacy host-based selection working via the transitional fallback in
  airflow_local_settings.py until the chain is removed (tracked by the meta issue), so existing
  configs are unaffected.

What

• Add OpensearchRemoteLogIO.from_config() in
  providers/opensearch/src/airflow/providers/opensearch/log/os_task_handler.py, mirroring the
  legacy branch:
  

  airflow/airflow-core/src/airflow/config_templates/airflow_local_settings.py

  Lines 349 to 379 in 104ad12

  	elif OPENSEARCH_HOST:
  	from airflow.providers.opensearch.log.os_task_handler import OpensearchRemoteLogIO
  	OPENSEARCH_PORT = conf.getint("opensearch", "PORT", fallback=9200)
  	OPENSEARCH_USERNAME: str = conf.get_mandatory_value("opensearch", "USERNAME")
  	OPENSEARCH_PASSWORD: str = conf.get_mandatory_value("opensearch", "PASSWORD")
  	OPENSEARCH_WRITE_STDOUT: bool = conf.getboolean("opensearch", "WRITE_STDOUT")
  	OPENSEARCH_WRITE_TO_OS: bool = conf.getboolean("opensearch", "WRITE_TO_OS")
  	OPENSEARCH_JSON_FORMAT: bool = conf.getboolean("opensearch", "JSON_FORMAT")
  	OPENSEARCH_TARGET_INDEX: str = conf.get_mandatory_value("opensearch", "TARGET_INDEX")
  	OPENSEARCH_HOST_FIELD: str = conf.get_mandatory_value("opensearch", "HOST_FIELD")
  	OPENSEARCH_OFFSET_FIELD: str = conf.get_mandatory_value("opensearch", "OFFSET_FIELD")
  	OPENSEARCH_LOG_ID_TEMPLATE: str = conf.get("opensearch", "LOG_ID_TEMPLATE", fallback="") or (
  	"{dag_id}-{task_id}-{run_id}-{map_index}-{try_number}"
  	)
  	REMOTE_TASK_LOG = OpensearchRemoteLogIO(
  	host=OPENSEARCH_HOST,
  	port=OPENSEARCH_PORT,
  	username=OPENSEARCH_USERNAME,
  	password=OPENSEARCH_PASSWORD,
  	target_index=OPENSEARCH_TARGET_INDEX,
  	write_stdout=OPENSEARCH_WRITE_STDOUT,
  	write_to_opensearch=OPENSEARCH_WRITE_TO_OS,
  	offset_field=OPENSEARCH_OFFSET_FIELD,
  	host_field=OPENSEARCH_HOST_FIELD,
  	base_log_folder=BASE_LOG_FOLDER,
  	delete_local_copy=delete_local_copy,
  	json_format=OPENSEARCH_JSON_FORMAT,
  	log_id_template=OPENSEARCH_LOG_ID_TEMPLATE,
  	)

  
  — reading the [opensearch] options the branch reads (host, port, username,
  password, target_index, write_stdout, write_to_os, json_format, host_field,
  offset_field, and log_id_template with its
  {dag_id}-{task_id}-{run_id}-{map_index}-{try_number} fallback) plus
  [logging] base_log_folder (with expanduser) and [logging] delete_local_logs, so
  behavior is unchanged for existing configs. Note the legacy branch does not merge
  remote_task_handler_kwargs IO-kwargs for this backend — mirror that too.
• Register the opensearch scheme under a remote-logging: section in
  providers/opensearch/provider.yaml and mirror it in
  providers/opensearch/src/airflow/providers/opensearch/get_provider_info.py.
• Document the remote_base_log_folder = opensearch:// form in the provider's logging docs.
• Add tests mirroring TestS3RemoteLogIOFromConfig in
  providers/amazon/tests/unit/amazon/aws/log/test_s3_task_handler.py.
• Verify end to end with a real system test: set up the actual backend yourself (a real
  OpenSearch cluster or a local one, e.g. via Docker), run a task with remote logging enabled,
  and confirm logs are written and read back through the new dispatch path. Include the setup
  and verification results in the PR description.

Reference

Merged examples to follow: #69817 (s3), #69816 (cloudwatch). If from_config raises on a bad
config, the shared factory falls back to the legacy path, so this is not a breaking change.

[FrankYang0529]

I would like to handle this one. Thank you.