Simplify creating multi-arch image

.github/workflows/multi-arch-image.yml

@@ -0,0 +1,27 @@
+name: Build
+
+on:
+  workflow_dispatch:
+  push:
+  pull_request:
+
+jobs:
+  image:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v2
+    - name: Pull manylinux images
+      run: |
+        for arch in x86_64 aarch64 ppc64le; do
+          docker pull quay.io/pypa/manylinux2014_$arch
+          docker tag quay.io/pypa/manylinux2014_$arch ghcr.io/spack/manylinux2014:latest-$arch
+          docker push ghcr.io/spack/manylinux2014:latest-$arch
+        done
+
+        docker manifest create ghcr.io/spack/manylinux2014:example \
+          ghcr.io/spack/manylinux2014:latest-x86_64 \
+          ghcr.io/spack/manylinux2014:latest-aarch64 \
+          ghcr.io/spack/manylinux2014:latest-ppc64le
+
+        docker login ghcr.io -u ${{ secrets.GITHUB_ACTOR }} -p ${{ secrets.GITHUB_TOKEN }}
+        docker manifest push ghcr.io/spack/manylinux2014:example