ci: Add test workflow for enabling containerd snapshotter

Author: camh-

.github/workflows/test.yaml

@@ -0,0 +1,20 @@
+name: test docker containerd snapshotter setup
+
+on:
+  push:
+    branches:
+      - test/*
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    steps:
+    - run: |
+        id -a
+        { cat /etc/docker/daemon.json 2>/dev/null || echo '{}'; } | \
+        jq '.features += {"containerd-snapshotter": true}' > /tmp/daemon.json
+        mv /tmp/daemon.json /etc/docker/daemon.json
+        systemctl restart docker
+    - run: ./bin/make build-oci OCI_PLATFORM=linux/amd64,linux/arm64
+    - run: docker images
+    - run: docker inspect foxygoat/flapjak