Migrate CI from Travis to GitHub Actions

- Add .github/workflows/unit-tests.yml calling shared reusable workflow
- Replace Travis badge in README.md with GitHub Actions badge
- Delete .travis.yml

Author: Copilot

.github/workflows/unit-tests.yml

@@ -0,0 +1,17 @@
+name: Unit Tests
+
+on:
+  push:
+  pull_request:
+    branches:
+      - main
+  workflow_dispatch:
+
+jobs:
+  tests:
+    uses: logstash-plugins/.ci/.github/workflows/unit-tests.yml@1.x
+    concurrency:
+      group: ${{ github.workflow }}-${{ github.ref }}
+      cancel-in-progress: ${{ github.ref != 'refs/heads/main' }}
+    with:
+      timeout-minutes: 60

.travis.yml

@@ -1,6 +1,6 @@
 # Logstash Plugin
 
-[![Travis Build Status](https://travis-ci.com/logstash-plugins/logstash-input-beats.svg)](https://travis-ci.com/logstash-plugins/logstash-input-beats)
+[![Unit Tests](https://github.com/logstash-plugins/logstash-input-beats/actions/workflows/unit-tests.yml/badge.svg)](https://github.com/logstash-plugins/logstash-input-beats/actions/workflows/unit-tests.yml)
 
 This is a plugin for [Logstash](https://github.com/elastic/logstash).