ci: keep ibkr gateway ssh tunnel alive

[Pigbibi]

Summary

• add SSH keepalive flags to gcloud compute ssh/scp through IAP
• reduce chance of long deploy tunnels dropping during docker compose build

Test Plan

• bash tests/test_workflow_shared_config.sh
• ruby -e 'require "yaml"; YAML.load_file(".github/workflows/main.yml")'\n- git diff --check