add GitHub action for publishing plugin

.github/workflows/publish-plugin.yml

@@ -0,0 +1,23 @@
+name: Publish to the Gradle Plugin Portal
+
+on: [workflow_dispatch]
+
+jobs:
+  publish:
+    runs-on: ubuntu-latest
+    env:
+      GRADLE_PUBLISH_KEY: ${{ secrets.GRADLE_PUBLISH_KEY }}
+      GRADLE_PUBLISH_SECRET: ${{ secrets.GRADLE_PUBLISH_SECRET }}
+    steps:
+      - name: Git checkout
+        uses: actions/checkout@v3
+      - name: Set up JDK 17
+        uses: actions/setup-java@v2
+        with:
+          cache: gradle
+          distribution: temurin
+          java-version: 17
+      - name: Create gradle.properties
+        run: echo -e "gradle.publish.key=$GRADLE_PUBLISH_KEY\ngradle.publish.secret=$GRADLE_PUBLISH_SECRET" > gradle.properties
+      - name: Build with Gradle
+        run: ./gradlew build -x test publishPlugins