Enable build on GitHub Actions

Author: jabby

.github/workflows/build.yml

@@ -0,0 +1,46 @@
+name: GitLab4J CI
+
+on:
+  push:
+    branches-ignore:
+      - 'dependabot/**'
+  pull_request:
+    types: [opened, synchronize, reopened, ready_for_review]
+
+jobs:
+
+  build-jdk8:
+    name: "Build JDK 8"
+    runs-on: ubuntu-latest
+    services:
+      gitlab-instance:
+        image: gitlab/gitlab-ce:12.9.2-ce.0
+        env:
+          GITLAB_OMNIBUS_CONFIG: gitlab_rails['initial_root_password']="password";gitlab_rails['lfs_enabled']=false;
+        ports:
+          - 8090:80
+    steps:
+      - uses: actions/checkout@v2
+        with:
+          fetch-depth: 0
+      - name: Set up JDK 8
+        uses: actions/setup-java@v2
+        with:
+          distribution: adopt-hotspot
+          java-version: 8
+      - name: Get Date
+        id: get-date
+        run: |
+          echo "::set-output name=date::$(/bin/date -u "+%Y-%m")"
+        shell: bash
+      - name: Cache Maven Repository
+        id: cache-maven
+        uses: actions/cache@v2
+        with:
+          path: ~/.m2/repository
+          # refresh cache every month to avoid unlimited growth
+          key: gitlab4jmaven-${{ steps.get-date.outputs.date }}
+      - name: GitLab4j verify
+        id: gitlab4j-verify
+        run: |
+          ./mvnw integration-test -B -V -Dmaven.javadoc.skip=true