Document REMOTE_TASK_LOG/DEFAULT_REMOTE_CONN_ID for custom logging configs

[anmolxlight]

Fixes #71768

Problem

With [logging] remote_logging = True and a user-defined logging_config_class, Airflow 3.2.x discovers the remote task log handler by reading two module-level attributes from the user's module (discover_remote_log_handler in shared/logging/src/airflow_shared/logging/remote.py):

• REMOTE_TASK_LOG
• DEFAULT_REMOTE_CONN_ID

If REMOTE_TASK_LOG is missing, the scheduler warns Remote log handler could not be loaded; logs will be available locally only. and task logs are never uploaded to the remote backend. The 3.2.2 documentation did not mention these attributes at all, so users migrating from 2.x (where a plain extended LOGGING_CONFIG dict was enough) hit this silently. The section already exists on main (and shipped in 3.3.x docs); this backports it to the v3-2-test branch so the 3.2 docs match.

Change

Backport the "Custom logging configs and remote logging" section from main into airflow-core/docs/administration-and-deployment/logging-monitoring/advanced-logging-configuration.rst, including:

• the two required module-level attributes and what they do
• the exact startup warning users see when REMOTE_TASK_LOG is missing
• a working MyRemoteLogIO example
• the note about defining it in your own module rather than re-exporting from airflow_local_settings

Docs-only change; verified the referenced API (airflow.logging.remote.RemoteLogIO, discovery of both globals) exists on the v3-2-test branch.

[uros-b]

LGTM