Migrate CI from Travis to GitHub Actions (main branch)

[Copilot]

This migrates main from Travis to GitHub Actions while preserving the test coverage defined by the fully-resolved Travis config. The resolved Travis setup was unit-tests only, so the PR adds only the corresponding reusable GHA workflow and removes Travis-specific wiring.

• Scope

  • Targets main only
  • Replaces Travis CI with GitHub Actions shared reusables from logstash-plugins/.ci@1.x

• Resolved Travis → GHA parity

  Travis matrix entry	GHA coverage
  ELASTIC_STACK_VERSION=9.current DOCKER_ENV=dockerjdk21.env	unit-tests.yml reusable
  ELASTIC_STACK_VERSION=9.previous DOCKER_ENV=dockerjdk21.env	unit-tests.yml reusable
  ELASTIC_STACK_VERSION=8.current DOCKER_ENV=dockerjdk21.env	unit-tests.yml reusable
  SNAPSHOT=true ELASTIC_STACK_VERSION=main DOCKER_ENV=dockerjdk21.env	unit-tests.yml reusable
  SNAPSHOT=true ELASTIC_STACK_VERSION=9.current DOCKER_ENV=dockerjdk21.env	unit-tests.yml reusable
  SNAPSHOT=true ELASTIC_STACK_VERSION=9.previous DOCKER_ENV=dockerjdk21.env	unit-tests.yml reusable
  SNAPSHOT=true ELASTIC_STACK_VERSION=8.current DOCKER_ENV=dockerjdk21.env	unit-tests.yml reusable

  No resolved Travis entries enabled:

  • INTEGRATION=true
  • SECURE_INTEGRATION=true
  • HAS_PERFORMANCE_TESTS=1

  As a result, no integration / secure-integration / performance workflow was added.

• Workflow changes

  • Added .github/workflows/unit-tests.yml
  • Uses logstash-plugins/.ci/.github/workflows/unit-tests.yml@1.x
  • Preserves the standard push, pull_request, workflow_dispatch, and default-branch scheduled matrix shape
  • Includes secrets: inherit on both caller jobs
  • Sets explicit permissions: contents: read

• README badges

  • Replaced the Travis badge with the Unit Tests GitHub Actions badge for main

• Travis removal

  • Deleted .travis.yml
  • No additional Travis-only files were present to remove

• Env / harness reconciliation

  • Resolved Travis config did not define plugin-specific env overrides beyond the inherited unit-test matrix variables already handled by the reusable workflow
  • Repository .ci/ does not vendor plugin-specific harness scripts requiring modernization or extra workflow env injection

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