First attempt at caching the image builds

.github/workflows/docker.yml

@@ -71,6 +71,16 @@ jobs:
 
       - name: Set up Docker Buildx
         uses: docker/setup-buildx-action@v2.9.0
+        with:
+          install: true
+
+      - name: Cache Docker layers
+        uses: actions/cache@v3
+        with:
+          path: /tmp/.buildx-cache
+          key: multi-buildx-${{ matrix.platform }}-${{ hashFiles('requirements*.txt') }}
+          restore-keys: |
+            multi-buildx-${{ matrix.platform }}
 
       - name: Login to Docker Hub
         uses: docker/login-action@v2.2.0
@@ -87,6 +97,10 @@ jobs:
           platforms: ${{ matrix.platform }}
           labels: ${{ steps.meta.outputs.labels }}
           outputs: type=image,name=${{ env.REGISTRY_IMAGE }},push-by-digest=true,name-canonical=true,push=true
+          cache-from: type=local,src=/tmp/.buildx-cache
+          # More: https://github.com/moby/buildkit#--export-cache-options
+          # And: https://github.com/docker/buildx#--cache-tonametypetypekeyvalue
+          cache-to: type=local,mode=max,dest=/tmp/.buildx-cache-new
 
       - name: Export digest
         run: |
@@ -102,6 +116,11 @@ jobs:
           if-no-files-found: error
           retention-days: 1
 
+      - name: Move cache
+        run: |
+          rm -rf /tmp/.buildx-cache
+          mv /tmp/.buildx-cache-new /tmp/.buildx-cache
+
   merge:
     runs-on: ubuntu-latest
     needs: