ci: add GPG setup for signing

Signed-off-by: Jendrik Johannes <[email protected]>

.github/workflows/flow-deploy-release-artifact.yaml

@@ -34,6 +34,28 @@ jobs:
       - name: Setup Gradle
         uses: gradle/actions/setup-gradle@d156388eb19639ec20ade50009f3d199ce1e2808 # v4.1.0
 
+      - name: Install GnuPG Tools
+        run: |
+          if ! command -v gpg2 >/dev/null 2>&1; then
+            echo "::group::Updating APT Repository Indices"
+              sudo apt update
+            echo "::endgroup::"
+            echo "::group::Installing GnuPG Tools"
+              sudo apt install -y gnupg2
+            echo "::endgroup::"
+          fi
+
+      - name: Import GPG key
+        id: gpg_key
+        uses: step-security/ghaction-import-gpg@6c8fe4d0126a59d57c21f87c9ae5dd3451fa3cca # v6.1.0
+        with:
+          gpg_private_key: ${{ secrets.GPG_KEY_CONTENTS }}
+          passphrase: ${{ secrets.GPG_KEY_PASSPHRASE }}
+          git_config_global: true
+          git_user_signingkey: true
+          git_commit_gpgsign: true
+          git_tag_gpgsign: true
+
       - name: Gradle Plugin Portal Release
         env:
           GRADLE_PUBLISH_KEY: ${{ secrets.GRADLE_PUBLISH_KEY }}