Fix OpenSearch remote logging crash if port is empty

[FrankYang0529]

Followup PR for #70295 (comment).

Why

• [opensearch] port declares default: "" in provider.yaml, so the key always resolves and conf.getint("opensearch", "PORT", fallback=9200) never reaches its fallback. The default value "" make it raise ValueError on int("").

How

• Read [opensearch] port as a string and convert explicitly, treating an empty value as "unset". An unset port still resolves to 9200.

Verification

• uv run --project providers/opensearch pytest airflow-core/tests/unit/config_templates/test_airflow_local_settings.py
• env -u AIRFLOW__OPENSEARCH__PORT AIRFLOW__LOGGING__REMOTE_LOGGING=True AIRFLOW__OPENSEARCH__HOST=https://opensearch.example.com uv run --project providers/opensearch airflow version
  • This command fails on main branch, but pass in this PR.

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

• Yes - Claude Code

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