Add GitHub Actions workflow for Hangar publication

Introduce a new GitHub Actions workflow to automate the publishing process to Hangar upon release events. This workflow checks out the repo, sets up JDK 21, and runs Gradle to publish publications to Hangar.

.github/workflows/hangar-publish.yml

@@ -0,0 +1,24 @@
+name: Hangar Publish
+
+on:
+  release:
+    types:
+      - prereleased
+      - released
+
+jobs:
+  build:
+    env:
+      HANGAR_API_TOKEN: ${{ secrets.HANGAR_API_TOKEN }}
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - name: Set up JDK 21
+        uses: actions/setup-java@v4
+        with:
+          java-version: '21'
+          distribution: 'temurin'
+      - name: Publish with Gradle to Hangar
+        uses: gradle/actions/setup-gradle@v3
+        with:
+          arguments: publishAllPublicationsToHangar