update to sign step to sign into dockerhub first

Author: tamalerhino

.github/workflows/ci.yml

@@ -79,6 +79,11 @@ jobs:
     needs: trivy
 
     steps:
+      - name: Login to Dockerhub
+        uses: docker/login-action@v2
+        with:
+          username: ${{ secrets.DOCKER_USERNAME }}
+          password: ${{ secrets.DOCKER_PASSWORD }}
       - name: Install Cosign
         uses: sigstore/[email protected]
       - name: Sign Container Image