Migrate main-branch CI from Travis to GitHub Actions using reusable plugin workflows

[Copilot]

This replaces Travis on main with GitHub Actions while preserving the same test intent: unit and Kafka-backed integration execution. The migration uses logstash-plugins/.ci@1.x reusable workflows and removes Travis-era wiring from this repo.

• Workflow migration (unit + integration)

  • Added:
    • .github/workflows/unit-tests.yml
    • .github/workflows/integration-tests.yml
  • Both workflows use the shared reusable workflows on @1.x, include scheduled matrix fan-out for active branches, and forward repo/org secrets with secrets: inherit.
  • Slack notifications are explicitly disabled (notify-slack: false) per plugin requirement.
  • Added least-privilege token scope:
    • permissions: contents: read

• Preserve plugin-specific integration behavior

  • Added repo-local .ci/run.sh override so reusable docker-run.sh executes the same test split expected by this plugin:
    • non-integration: bundle exec rake test
    • integration: Kafka setup + bundle exec rspec --tag integration + teardown trap
  • Script paths are anchored to repo root for stable execution regardless of cwd.

• Repository cleanup

  • Deleted .travis.yml.
  • Replaced Travis badge in README.md with GHA badges for unit and integration workflows (?branch=main).

# .ci/run.sh behavior used by reusable docker-run.sh
if [ "${INTEGRATION}" = "true" ]; then
  trap "${REPO_ROOT}/kafka_test_teardown.sh" EXIT
  "${REPO_ROOT}/kafka_test_setup.sh"
  bundle exec rspec --tag integration
else
  bundle exec rake test
fi

• Fixes Migrate CI from Travis to GitHub Actions (main branch) #348

[donoghuc]

new files added to support migration and shared workflows. the failures are unrelated to the migration. merging.