Add an action to deploy to Github Packages.

.github/workflows/gradle-publish.yml

@@ -0,0 +1,32 @@
+# This workflow will build a package using Gradle and then publish it to GitHub
+# packages when a release is created
+
+name: Gradle Package
+
+on:
+  release:
+    types: [created]
+
+jobs:
+  build:
+
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+      packages: write
+
+    steps:
+    - uses: actions/checkout@v2
+    - name: Set up JDK 16
+      uses: actions/setup-java@v2
+      with:
+        java-version: '16'
+        distribution: 'adopt'
+        server-id: github
+        settings-path: ${{ github.workspace }}
+
+    - name: Build with Gradle
+      run: ./gradlew build -x test
+
+    - name: Publish to GitHub Packages
+      run: ./gradlew publish -PmavenReleaseRepoUrl="https://maven.pkg.github.com/css4j/xml-dtd" -PmavenRepoUsername=${{ github.actor }} -PmavenRepoPassword=${{ secrets.GITHUB_TOKEN }}