Use github cache for docker layers (#1164)

Cache the build layers between github action builds to reduce time
required.

.github/workflows/docker-image.yml

@@ -56,7 +56,14 @@ jobs:
         uses: docker/setup-buildx-action@v1
         with:
           driver-opts: image=moby/buildkit:master
-
+      -
+        name: Cache Docker layers
+        uses: actions/cache@v2
+        with:
+          path: /tmp/.buildx-cache
+          key: ${{ runner.os }}-buildx-${{ github.sha }}
+          restore-keys: |
+            ${{ runner.os }}-buildx-
       -
         name: Check have credentials
         id: have_credentials
@@ -87,6 +94,8 @@ jobs:
             org.opencontainers.image.created=${{ steps.prep.outputs.created }}
             org.opencontainers.image.revision=${{ github.sha }}
             org.opencontainers.image.licenses=${{ github.event.repository.license.spdx_id }}
+          cache-from: type=local,src=/tmp/.buildx-cache
+          cache-to: type=local,dest=/tmp/.buildx-cache,mode=max
       -
         name: Image digest
         run: echo ${{ steps.docker_build.outputs.digest }}