ci: push multi-arch images with manifest-tool

Instead of buildah.

- Simplified workflow: manifest-tool provides a more straightforward command-line interface for creating manifest lists
- Better integration: manifest-tool is specifically designed for manifest list/OCI index creation and management
- Cross-platform compatibility: Works with both Docker v2.2 manifest lists and OCI v1 indexes
- Template-based approach: The --template and --platforms flags provide a cleaner way to specify multi-arch images

.github/workflows/main.yml

@@ -1547,6 +1547,13 @@ jobs:
           username: ${{ secrets.DOCKER_USER }}
           password: ${{ secrets.DOCKER_PASS }}
 
+      - name: Install manifest-tool
+        if: github.ref == 'refs/heads/master'
+        run: |
+          wget https://github.com/estesp/manifest-tool/releases/latest/download/binaries-manifest-tool.tar.gz -O - | tar -xz
+          sudo cp manifest-tool-linux-amd64 /usr/local/bin/manifest-tool
+          sudo chmod +x /usr/local/bin/manifest-tool
+
       - name: deploy-multi-arch
         if: github.ref == 'refs/heads/master'
         run: |