Create GitHub Actions build script (#1)

* Create gradle.yml

.github/workflows/gradle.yml

@@ -0,0 +1,45 @@
+# This workflow will build a Java project with Gradle
+# For more information see: https://help.github.com/actions/language-and-framework-guides/building-and-testing-java-with-gradle
+
+name: Build SlimeVR Server with Gradle
+
+on:
+  push:
+    branches: [ main ]
+  pull_request:
+    branches: [ main ]
+
+jobs:
+  build:
+
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v2.3.4
+
+    - name: Clone Slime Java Commons
+      uses: actions/checkout@v2.3.4
+      with:
+        repository: Eirenliel/slime-java-commons
+        # Relative path under $GITHUB_WORKSPACE to place the repository
+        path: Slime Java Commons
+
+    - name: Set up JDK 11
+      uses: actions/setup-java@v2.1.0
+      with:
+        java-version: '11'
+        distribution: 'adopt'
+
+    - name: Grant execute permission for gradlew
+      run: chmod +x gradlew
+
+    - name: Build with Gradle
+      run: ./gradlew clean serverJar
+
+    - name: Upload the Server JAR as a Build Artifact
+      uses: actions/upload-artifact@v2.2.4
+      with:
+        # Artifact name
+        name: "SlimeVR-Server" # optional, default is artifact
+        # A file, directory or wildcard pattern that describes what to upload
+        path: build/libs/*