Migrate CI from Travis to GitHub Actions (main branch)

[Copilot]

This migrates CI on main from Travis to reusable GitHub Actions workflows, preserving the effective Travis test coverage after resolving imported .travis.yml config. For this plugin, Travis resolved to unit-test coverage only, so the migration adds only the unit workflow and retires Travis config.

• CI workflow migration (parity-first)

  • Added .github/workflows/unit-tests.yml using logstash-plugins/.ci/.github/workflows/unit-tests.yml@1.x
  • Kept required caller shape: push/pull_request on main, daily schedule, workflow_dispatch, tests + scheduled jobs
  • Added secrets: inherit on both jobs and ref: ${{ matrix.branch }} for scheduled fan-out
  • Set timeout-minutes: 60 and explicit permissions: contents: read

• Repository cleanup

  • Removed .travis.yml (Travis retired for this branch)

• README status badges

  • Replaced Travis badge with GitHub Actions badge for unit-tests.yml scoped to ?branch=main

• Travis-to-GHA mapping (resolved config)

  • Travis base matrix env jobs (ELASTIC_STACK_VERSION / SNAPSHOT variants) → Unit Tests reusable workflow
  • No INTEGRATION=true / SECURE_INTEGRATION=true / plugin-level performance enablement detected → no additional workflow files added

jobs:
  tests:
    uses: logstash-plugins/.ci/.github/workflows/unit-tests.yml@1.x
    secrets: inherit
    with:
      timeout-minutes: 60

  scheduled:
    strategy:
      matrix:
        branch: [main]
    uses: logstash-plugins/.ci/.github/workflows/unit-tests.yml@1.x
    secrets: inherit
    with:
      ref: ${{ matrix.branch }}
      timeout-minutes: 60