Migrate CI from Travis to GitHub Actions (6.x branch)

[Copilot]

This PR migrates CI for the 6.x branch from Travis to GitHub Actions, preserving the Travis test coverage exactly (no dropped matrix entries, no extra test types). It introduces the branch-symmetric reusable-workflow consumer pattern required for active branches (6.x, main), including scheduled fan-out via matrix ref.

• Scope / branch targeting

  • Targets 6.x only.
  • Uses reusable workflows from logstash-plugins/.ci@1.x.

• Travis matrix parity (resolved import chain)

  • Resolved .travis.yml import:
    • logstash-plugins/.ci:travis/travis.yml@1.x
    • which imports travis/defaults.yml, travis/matrix.yml, travis/exec.yml
  • Resolved Travis test matrix entries:

    Travis env combo	GHA coverage
    ELASTIC_STACK_VERSION=9.current DOCKER_ENV=dockerjdk21.env	Unit Tests reusable matrix
    ELASTIC_STACK_VERSION=9.previous DOCKER_ENV=dockerjdk21.env	Unit Tests reusable matrix
    ELASTIC_STACK_VERSION=8.current DOCKER_ENV=dockerjdk21.env	Unit Tests reusable matrix
    SNAPSHOT=true ELASTIC_STACK_VERSION=main DOCKER_ENV=dockerjdk21.env	Unit Tests reusable matrix
    SNAPSHOT=true ELASTIC_STACK_VERSION=9.current DOCKER_ENV=dockerjdk21.env	Unit Tests reusable matrix
    SNAPSHOT=true ELASTIC_STACK_VERSION=9.previous DOCKER_ENV=dockerjdk21.env	Unit Tests reusable matrix
    SNAPSHOT=true ELASTIC_STACK_VERSION=8.current DOCKER_ENV=dockerjdk21.env	Unit Tests reusable matrix

  • No Travis signals for INTEGRATION=true, SECURE_INTEGRATION=true, or performance gating in this plugin config, so no corresponding workflows were added.

• Workflow files added

  • Added: .github/workflows/unit-tests.yml

• README badge migration

  • Replaced Travis badge with branch-specific GHA badge:
    • unit-tests.yml/badge.svg?branch=6.x

• Travis retirement

  • Deleted: .travis.yml
  • No additional Travis-only directories/files were present.

• Vendored .ci/ scripts review

  • Existing .ci/ scripts were reviewed for Compose v1 usage; no stale docker-compose invocations found, so no script modernization/deletion was required.

jobs:
  tests:
    if: github.event_name != 'schedule'
    uses: logstash-plugins/.ci/.github/workflows/unit-tests.yml@1.x
    with:
      timeout-minutes: 60

  scheduled:
    if: github.event_name == 'schedule'
    strategy:
      matrix:
        branch: ['6.x', main]
    uses: logstash-plugins/.ci/.github/workflows/unit-tests.yml@1.x
    with:
      ref: ${{ matrix.branch }}
      timeout-minutes: 60